I agree, but I hope you weren’t talking to me. I do not suspect that my neighbors are peeping Toms who want my shades open for voyeuristic reasons. That is a possibility raised by some other posters in this thread, which I happen not to agree with.
BTW, since someone indirectly raised the question, I’m male.
If it was me I would not start opening my blinds, and I would start coming and going at odd times of the day and night, remove any lawn or house decorations I already have, and do whatever possible to make them more curious about what’s going on in my house.
If I remember my sitcoms correctly, this is the kind of situation where you convince the neighbors their is a large sum of money or a dead body located right where you need to dig a hole for your new inground hot tub.
If it were me, I’d probably vent on a message board, but otherwise try to ignore the weird request from the neighbors. 
In the past two places I’ve lived in, covering 20+ years, I’ve driven daily past neighboring homes and frequently gone on walks by them. I couldn’t begin to describe who kept their blinds/shades closed and who kept them open (and on what schedule). In my opinion, taking note of such things (and being able to quantify the percentage of neighbors who fall in each category) would be unusual. Noticing patterns and being sufficiently disturbed by them to suggest to the neighbors that they do things differently goes beyond unusual and at least verges on creepy.
Cool. Different people have different beliefs as to what is or is not unusual.
I guess i know that the next door neighbors often raise the shade of the upstairs window that faces my house. I know that because when i sit at my desk and look idly out my window, the movement of the shade going up sometimes catches my eye. Looking at that window right now, i can’t actually see anything inside the house. If i really peer at it, i can make out reflections of some trees.
The downstairs shades are all down. And this is literally the first time I’ve noticed that.
Put me in the category of, “i think it’s weird to notice.”
This would be my solution of choice.
Kind of an aside, but in the past, when I have looked for a place to live, one of several factors I have considered is whether the community and its residents appear to be the sort of place I would be comfortable with. No - not looking for anything Stepfordy or exclusionary. But if I want an old car up on blocks in my driveway, I don’t move into a fancy neighborhood w/ an HOA. Or if I want my house and yard pristine and manicured, I don’t move into a slum with decrepit buildings and weed-filled yards. Lots of variability between such extremes.
The idea that a majority of folk in a neighborhood might favor some outward signs of openness and friendliness - well, many of you likely disagree - but that doesn’t strike me as horrific. I regularly find it curious when people move into an area where the majority of folk have certain expectations, and act shocked that their behaving differently is noticed and remarked upon.
I agree with what you’re saying, but I would draw the line at neighbors telling other neighbors how to maintain their house. If it’s an HOA issue, they should tell the HOA and let the HOA decide if they want to pursue it. Otherwise, neighbors should keep their preferences to themselves.
But certainly neighbors will talk amongst each other and gossip just like everyone does. If one neighbor has a significantly different philosophy about maintenance or curb appeal compared to the other neighbors, then other neighbors may have a poor opinion of the person or express those opinions to other people. That’s just human nature. The neighbor in question shouldn’t be surprised that other neighbors don’t like a house if it sticks out like a sore thumb. (To be clear, this is just a general comment, not a comment about the OP. I don’t think the OP is doing anything wrong.)
If this duplex is anything like the ones I see in Trenton, I can think of one possible reason:
Those duplexes look like single-family homes with the peaked roof overhead and two front doors. In Trenton they often have two different kinds of siding on them, with a vertical centerline, making it look weirdly like two unrelated half-houses squished together. I can imagine if someone is in a home like that (perhaps without the two-tone siding treatment) they might want their home to appear more uniform and less “split” from the front. It’s certainly none of their business–they knew what they were getting into with that kind of home.
And those particular houses in Trenton are right on the sidewalk: people can stop and stare right in. That’s not cool. So, if I lived in one of those homes I’d have my first-floor blinds closed all the time.
Of course, there are dozens of other reasons to close the blinds. My wife’s baby grand piano is next to the front window in our living room and we don’t want it bathed in sunlight, so we keep that window permanently covered.
Just to be clear, the HOA is just a two-household HOA between me and my neighbors who own the other side of the twin only. We’re in an older neighborhood that was built before subdivisions and HOAs were a thing, but for whatever reason there was an empty lot here which a builder bought a couple of years ago, built our places, and set them up with an HOA.
I didn’t grow up in an area with HOAs and don’t believe I ever heard of the concept until I was about thirty. And when I did first hear of the concept, my immediate reaction was “that’s ridiculous! Why would anyone ever agree to that? What do you mean, I can’t paint my house a certain color or put up window shutters? It’s my house!” Eventually, I did kind of grasp the concept that people don’t want cars up on cinder blocks in the neighbor’s front yard, or even pink flamingoes or a house painted bright pink, but the idea that someone would care whether or not I open my blinds still never occurred to me.
The neighbor doesn’t care whether or not your blinds are up or down. They’re being neighborly and letting you know that strangers are looking at your home. That is, be happy that they’re interested in helping you and your property stay safe. This is what good neighbors do and is the benefit of having nearby people aware of what’s happening when you’re not there.
No matter the reason, your home is the one attracting attention from people coming into the neighborhood.
I think I am confused now. In the OP , you described this as a “twin home” and linked an article that says
“But in a twin home situation, the lot line runs down the middle of the house.”
and later describes a twin home as
A twin home is two properties on two lots and a duplex is two properties on one lot.
I don’t understand why you would be in a two-household HOA if the two houses were on two separate lots. That seems more in line with that article’s description of a duplex :
A duplex is made up of two individual properties on one shared lot. Each side of the duplex may have a separate owner, but the owners must cooperate on landscaping, exterior maintenance, and more. A duplex is classified as a multifamily property, while a twin home is not.
I think it makes a difference , because if the houses are on two separate lots, then your neighbors have no more say in what you do that my neighbors have a say in what I do with my fully detached house on my own lot. But if you are essentially living in a two-unit condo, where you own your unit ( but share ownership of the land) , that might be a different situation.
This does change things since an HOA has the legal authority to enforce the covenants, and the covenants often have vague terms in it like “maintain the house in an attractive appearance”. A lot of the distain for HOAs comes from HOAs where the board is made up of a bunch of nosy, opinionated, busy-bodies who nit-pick homeowners over minor infractions, Not all HOAs are like that, but the ones who are can be annoying. Depending on the makeup of your HOA, your neighbors could have some legal authority to force you to maintain your house in a consistent way with the other houses. Some covenants have very specific things, like you can’t park your car in your driveway and your garage door can’t be left open for long periods of time. Your covenants could actually have something in it that says the blinds have to generally be open during the day. It’d be worth reading through the HOA covenants to find anything any requirements like that or vague, subjective terms like “unsightly appearance” that might affect your situation.
Technically it is a condo association. But I don’t think that makes a difference in this particular issue. There’s nothing in the agreement that says I have to open my blinds.
BTW, the two sides don’t have different siding. The entire thing is brick face and there is no visible vertical dividing line.
I had checked this when I moved in, because I was ordering window treatments, and it does specify that they have to be white or off-white. But I just checked again, and this is all it says about the windows:
I also searched for the word “appearance” and found this:
Hard to imagine my neighbors winning a victory over me in small claims court on the basis that my keeping my blinds closed “detracts from the appearance of the Condominium.”
Interesting; it seems like you’re the first poster in this thread taking at face value their statement that people keep asking them whether my place is available, despite the fact that no one has ever rung my doorbell to ask me about it–and I am home during the day a fair amount. What do you make of the fact that most others have expressed skepticism over this, particularly over the idea that someone told them they thought closed blinds = place for rent?
But they could claim that your keeping the blinds down “interferes” with their “quiet enjoyment”, since they allege that strangers keep asking them about occupancy of the other side of the duplex. And how can they possibly enjoy their home if they have to keep wondering what you’re doing behind those closed blinds? 
Just another reason to avoid HOAs like the plague.
(I agree with Pleonast’s clarification). So now that you know that your neighbors DO care, you have the choice of how you respond. I don’t think anyone would suggest you ought to allow your neighbors to direct every aspect of how you live in and maintain your home. But you might wonder whether you would get more mileage out of adapting SOME minimal behavior which will make others think you are a positive member of the neighborhood. Or, you could just say “Fuck them!” and be an iconoclast.
It is fine and dandy to say you don’t give a damn about your neighbors and don’t care what they think of you. But I think most people view living in a neighborhood as having some minor aspect of give and take. You never know when it might be useful for the folk across the street to notice that your home is being broken into, or that they’ll be willing to pick up your paper or water your pots while you are out of town. And you might derive some pleasure from doing the same to them.
My goal is to be and have what I call “Hey, neighbors!” When you see them, you smile, wave, ad sa, “Hey!” And pretty much leave it at that. I like to garden, and derive mild pleasure when a neighbor or passer by says my front yard looks nice. What I wish to avoid is being the guy that people talk about negatively. The guy with the barking dog/yard that looks like hell/who plays loud music late at night…
So I’d probably think of some little thing that would reflect their concerns. Maybe as little as moving a blind occasionally. I’d pick one that was really convenient and didn’t mess with the heat/AC, and move it when I left for work or when I returned. Of maybe I’d put a pot with plants out front, or hang something on my door. But that’s just me.
I open the blinds in the back of my house, and those that open to the back yard. The ones that open to the street are always closed (curtains actually, not blinds). I get plenty of light, thank you.