Those aren’t sandwiches, though. (Although Cincinnati chili dog would count.)
Oh, man, I loved Elsie’s. I only spend a couple months in Cambridge during the summer, but even just their regular hot dog (which I think was a buck at the time, c 1994) was fantastic. With only slight exaggeration, I felt like half my lunches while I was there were Elsies hot dogs. And only a buck!
Minneapolis has the Jucy Lucy
In Chicago, at the Maxwell Street Market (and elsewhere in the city) you can get “Mexican” hot dogs, dogs wrapped in bacon. This may have migrated from Mexico to California to Chicago.
Pulyk, don’t know if you are aware of the LTH forum but they have an article/discussion of the Jim Shoe
Yep, I know them very well. In fact, if you go to my post where I mention the Jim Shoe, you’ll see that it’s the same link as yours to LTH forum. 
I’m Binko on there. I don’t participate nearly as often as I used to, but I still post from time to time.
Your post on the hot dogs reminds me (although you touch on it with mentions of Mexicao and Cali) of Sonoran dogs that you’ll find in Southern Arizona. There’s a truck in Phoenix that does a good version, but I believe they’re more popular in the Tucson area. Related is the Baja California Tijauana dog, sometimes called “danger dogs.” You can see here. Cigars and Stripes in Berwyn serves up a nice version of these wrapped in a flour tortilla instead of a hot dog bun.
When I lived in Binghamton, NY, it was definitely the Spiedie (sometimes spelled in other, eccentric ways)
I used to send back there for Spiedie sauce, but I have since found that they sell it at the new supermarket near my home in Massachusetts (!) There must have been a splinter tribe of spiedie-eaters here in Massachusetts. I found records of a one-time spiedie restaurant in Melrose, MA. Otherwise, Spiedies are strictly a Southern-Tier NY affectation. They had them in Binghamtopn and the tri-cities, and in Ithaca, but not in Rochester.
Speaking of Rochester, Nick Tahou’s garbage plate not only isn’t a sandwich, it’s not universal. I’d suggest for a sandwich the Country Sweet/sal’s Birdland-style hot chicken sandwich. The sauce is unique, in that I’ve never encountered it outside Rochester. I used to send back there for Smitty’s Sauce, now sadly gone. But I can get Boss Sauce through the mail.
To tell the truth, I don’t know what the signature Boston sandwich would be. Lobster roll?
I’m sure Pepper Mill would say the signature sandwich from her part of NJ was the Taylor Pork Roll.
Ah, the good old Taylor Hameggn Cheese saltpepperketchup. Classic NJ breakfast food. Usually with a regular coffee, though I preferred mine without the sugar.
Generically, yes.
You can eat a lot of food in Atlanta from all kinds of cuisines but nothing much that just says “Only in Atlanta.”
But let me throw in a couple of local places that are most worthwhile, though you shouldn’t eat like this every day.
Ann’s Snack Bar – The Ghetto Burger.
And my personal favorite, The Varsity … “What’ll ya have?” “Two chili dogs, onion rings, Frosted Orange.” There’s other stuff on the menu but I’ve never gotten past this. (Have your money in your hand and your order on your mind.)
http://news.wabe.org/post/workers-varsity-learn-art-what-ll-ya-have
I had that hot sauce in a bottle here (I thought I still had it, but I must have tossed it when cleaning out the fridge a month ago.) I’m trying to remember where I bought it. It was either in a Wegman’s near Hershey, PA, or a Wegman’s in Binghamton, NY. I believe it was the Sal’s brand that I had. I remember it being a sweet, yellow, mustard-based sauce with visible red pepper in it, and I recall reading something about Birdland on it, which is what triggered my memory from your post.
My bet would be you got it in Binghamton. Hershey’s way too far afield for Rochester-based food. But I could believe that it made its way down to Binghamton.
That’s my guess, too, but I’m not 100% sure. I know I came back from both trips with local delicacies. Two brands of Spiedie sauce from Binghamton, and Zweigle’s Rochester white hots from Hershey. But the sauce could have been either. And I couldn’t score any Sahlen’s hot dogs at either location. 
(But I did eventually pick up a five-pound box from the Ted’s outpost in Phoenix to take back home.)
Yeah, looking online, I have availability for Sal’s in the Johnson City (Binghamton) Wegman’s, but not the one near Hershey.