Two custom bookplates I found in two books I was preparing to sell.
Found inside a copy of Vanishing Point by Patricia Wentworth. The text reads: "Black is the rave/Black is the rook/But Blacker the child/Who steals this book." Now there's a sentiment I wholeheartedly agree with. I think I'd substitute child for person to make it an all-encompassing warning for book thieves.
Found inside a copy of My Own Murderer (Julian Messner, 1940) by Richard Hull. A genie bookplate! I don't see many of those.