By all means lend your books. But whatever you do, don't lend them without bookplates!
In decades and centuries past, knowing who owned which book was an obvious matter of opening it. Pasted on the inside front cover would be the bookplate: a unique rectangular label bearing the owner's name, perhaps an illustration, and often the Latin words "Ex Libris" — a phrase used all over the world to mean "from the library of."
Our bookplates are traditionally made, and made to last. We use offset lithography with dense black printer's ink on bright, white, archival, acid free paper; each set boxed with accessories.