Have u ever found something weird in a book? In our library we find weird things people use as book marks all the time. Infact we have a whole drawer in lost property full of photos that people have left in books as book marks.
'Pommie Sarah' told me that she once found a piece of BACON in a book in the mobile library. Creative, but I tend to recommend book marks of the non-perishable variety. And less greasy.