Bookplates, for example. There are numerous bookplates in the digital collection. Here are a few of them, to whet your appetite.
Bookplate of Helen Louise Taylor, Cincinnati, Ohio
Bookplate of Charles Chaplin
Bookplate of English author Mrs. G. Linnaeus Banks
Bookplate of Bella C. Landauer with "Lend a hand" motto
Linocut circa 1925
Edward Penfield, bookplate designer
Bookplate of Jack London
Bookplate of artist Francis D. Millet
Bookplate of Buddy Lankes
Also, for the definitive blog on the world of bookplates, check out Lew Jaffe's Confessions of a Bookplate Junkie.