These are supposedly actual signs that have appeared at various locations...

On a door: "Push. If that doesn't work, pull. If that doesn't work, we must be closed."

Message on a leaflet: "If you cannot read, this leaflet will tell you how to get lessons."

Outside a photographer's studio: "Out to lunch: if not back by five, out for dinner also."

In a store: "Prices subject to change according to customer's attitude."

Next to a swimming pool: "Welcome to our ool. Notice there's no 'p' in it. Let's keep it that way."