Do you know what bookplates and ex-libris are? These prints or stamps that mark the book's ownership. Here is a twist: the Utopian Libraries project by a Russian artist Dmitry Babenko includes only bookplates of nonexistent libraries.
A Bibliophile’s Ex-Libris for 37.000 Books – The Bookplate of Sergey Vavilov with an Engraving of Félix Vallotton
I often find curious things just browsing tomes in old books stores. Here is an excellent example. This bookplate on a vintage book about engraving techniques of the 19th century momentarily attracted my attention.