To help with the Book Fair, I got my staff t-shirts that read "Guess What I'm Reading". Next year, we may go with "Got Books?"
Over the years I've accumulated many, many library/book oriented shirts. Of course I have "I cannot live without books" (Jefferson) and "Books, Cats, Life is Good". However, two of my favorites remain "To err is human. To forgive is not library policy." and George Bush saying "The best thing I ever did was to marry a librarian".
One I'd love to have? ABC-CLIO's "Question ^an Authority".