You must make sure the books will be available for the scheduled signing date. For maximum exposure and a good signing, the store will advertise the book signing in their magazine and that requires advance planning.
I had my first book signing at B/N in Charlottesville and it was publicized, however the books that were promised were held up since PA didn't allow returns from the distributor or the bookstore. This was a case where I had to buy my own books and place them on consignment with the store. They were congenial with me but held a grudge against PA. It was a red flag and would affect any PA published book with their stores. By the time I had my second signing with Borders in York, PA., PA had agreed to allow returns on certain books and mine was one of them, presumably due to my complaint. Borders ordered 40 copies and I had extra books on hand.
Although your book is not published by PA, I mention the above to alert you to potential problems. If your publisher is listed with a distributor with the normal return policy, there should be no problem assuming they have been ordered by the store and are in stock. Otherwise, be prepared to have your own supply available. You may not get a second chance for the signing.