Forgotten Bookmarks: A Bookseller's Collection of Odd Things Lost Between the Pages.
In Forgotten Bookmarks, Popek presents exactly what he found - an artifact in a book - and usually adds a transcription of any handwritten messages. Like Popek, we get to puzzle over the significance of the item and whether there is some specific reason why it was in the book. Many of the items must have been the first thing at hand when the reader stopped reading, but other seem to have more connection, such as a poem "A Prayer for My Daughter" found inside the book Cutting: Understanding and Overcoming Self-Mutilation. Family photos stuck in Bibles is easy to understand, and it seems natural to find a postcard of New York's East River Bridge in The Old New York Frontier. I liked that he found a baseball card of Pee Wee Reese in The Best of Baseball. I used to use a Lou Brock card as a bookmark.
Like Popek, we sometimes find items in books returned to the library, but they are usually checkout receipts or library-produced bookmarks. Because these books were borrowed instead of owned, the readers were probably more careful to remove items from them. Still, we find a leather bookmark or a tassel every now and then. They go to our lost and found, if you are looking for one you are missing.
Popek, Michael. Forgotten Bookmarks: A Bookseller's Collection of Odd Things Lost Between the Pages. Perigee Book, 2011. 182p. ISBN 9780399537011.