Here's Your Sign
A phrase coined by comedian Bill Engvall. The 'sign' should be worn by stupid people baring the warrning that they are infact stupid. When someone does something stupid, you can simply tell them 'Here's your sign...'
In the lost luggage section of an airport...

Bill Engvall: She said, "Can I help you?" I said, "Yes ma'am, you lost my luggage." She looked me right in the eye and said, "Has your plane landed yet?" "No, princess, I'm having an out-of-body experience! I'm just checking on it! Here's your sign."