Take a couple of medium or large binder clips. Clip to edge of poster board, use the hole in the handles to hang from nails on the window frame.
Yes, but why do it the easy way: https://www.staples.com/Velcro-Sticky-Back-Sticky-Tape-Black-15-Pack/product_VEK90069 when you can turn it into a SD ordeal?:rolleyes:
If that’s a concern, the sheets are long enough at 8 feet that they can sit directly on the floor inside the room and just lay against the blinds. That way they wouldn’t be visible from the outside.
:smack: Brilliant.
I’m reading this thread again and I’m not sure what to make of the whole “management won’t allow room darkening blinds” aspect. Is this actually the case? There are leased townhomes where the tenant is not allowed to put up blinds (since room-darkening blinds look no different from other blinds from the exterior, I’m going to assume that NO blinds are permitted)? This seems very odd. And a piece of posterboard would seem to be a lot less desirable to look at than a nice set of blinds.
Back to the question…I agree with those who suggest a tension rod. It’s easy to fashion hooks for the posterboard using binder clips and you don’t have to screw anything into the window frame/trim.
I think you’re all over-thinking and over-engineering.
The OP has the poster boards, and already has (or willing to install) nails on the wall above the window. The only issue is that holes in the poster board aren’t strong enough to take the weight.
The obvious solution would be to attach a harder, stronger material to the poster board and drill a hole in that. Or choose a flat plate that already has holes in it. The material could extend past the upper edge of the board, or not. So the question is, what material, and how to attach it.
If the poster board is foam, like this, I think most types of glue would work on it. As for material, metal braces like these would probably work. The larger the better, to distribute the weight. I’d use epoxy to attach it to the poster board. Or any scrap material you may have lying around should do - maybe a piece of plywood?
If the poster board is some kind of plastic, then that limits the types of glue that would work. But there are still many options. There are double-sided tapes and special epoxy adhesives that are specifically designed for plastic. Or you could use metal brackets like the above, but use two of them on both sides of the poster board, and use screws to compress the poster board between the brackets.
Damn, who is this nazi of a building manager? You have a condition. You can’t work from home without a solution. Blackout blinds, a completely reasonable and not the least bit unattractive, is a good, sane solution. And now you’re having to basically reinvent the wheel in a way that’s going to look like a kid’s project in your own home. This is the dumbest thing I’ve heard of in a while.
I assure you, building and apartment managers can be Nazis. They have a little power and a management company to appease. How the condos or apartments look from the street is important to them. It’s stupid but that’s how they are.
Hot glue a magnet to each corner of the window frame.
Put up the poster board.
Hot glue magnets on the poster board (on your side) corresponding to where the corner magnets are.
Draw unicorn on poster board with lots and lots on glitter.
Move the computer table to another wall.
WOW! You folks are incredibly creative while simultaneously being quite sensible!
There are more excellent ideas provided here than I’d ever expect to see. I’m going to try more than one of your suggestions when I’m able once again.
I deeply apologize for not being present here until now and thus not more directly responding and interacting, but my disabilities have been acting up more than usual. They’ll be much more manageable again in time, probably within a week or two, so please don’t worry.
Thank you all so incredibly much!! 
One option is to get a temporary shade like this:
It’s basically a cheap, paper shade that you can stick inside the window frame. They’re often used by people who buy a house which doesn’t have any window coverings and want something to block the windows. You can fold it up when you want the light, and let it down when you want it darlk.
They have those paper shades at Wal-Mart also. They are less than $5.