This demon will remind your friends of what might befall them should they neglect to return your books. His skull companion reinforces that, but even more so, do the little pair of boots you can make out behind him, hanging from the gibbet!
He comes from the prolific and skilled pen of the Norwegian-Danish illustrator and writer, Louis Moe (1857-1945).
I have altered his background just a little, and added the slogan. Your name will be added in the same gloriously gloomy font. The plates are 3-1/2 inches by 3-1/4 inches, and print six to a page.