Don't squeeze the Charmin and don't read the books, either
A friend of mine snapped this picture yesterday at a local antiques co-op. The shelf behind the hand-written sign was lined with well-worn children's books of no particular value. At first, my friend thought the seller must be an incredible book snob to post such a notice. Then he had another thought, that the books might contain material some might find offensive. If I'd been there, I would have asked the seller directly. Other theories?