Okay. I got THE friendliest guy ever.
He says that no, you don't have to buy the book there. He was like "noooo, of course not!" He says you should try to bring a reciept if you have one, just so they know you didn't like... smuggle their books off of the shelves and whatnot. But he said if you bought the book a while ago, that's fine and everything.
As for limitations, he said that it's typically up to the person doing the signing. Some people only want to sign one thing, and some will sign anything you put in front of them. He said the only times the B&N staff get involved in putting limitations on how many items you can get signed is if there are a ton of people, and they need to move things along, because to be fair they want everybody to get something. So he said unless there are like 2 bajillion people there, he didn't think it would be very strict.
He said that if there are any problems or questions, just talk to the security guards and explain to them what you want to do and they should be fine with it.
Yay for friendly man.
A work of art is an invitation to love.