I've had a book signing at B&N as well. They're very accommodating, and the Erie store was fabulous. They advertised it with signs ahead of time, set me up in a little area downstairs where I could have a mini-workshop, even gave me the stickers to show these were autographed copies!
When you have a book to promote, you send a letter to the store manager, with your book information sheet, so they can order some. Then find a mutual date. I'd recommend inviting friends and supporters to stop by, because a lot of times a booksigning is a fairly lonely event. You have to be able to reach out to folk wandering the bookstore and connect, to get them to come find out what your book's about.
It's STILL cool, tho.