Putting eyepatches on fire hydrant

Mr. Bernett refers to useless tricks in advertising and mentions putting eyepatches on fire hydrant as the example of the obvious trick. What does it really mean? Perhaps this speech figure has a certain background?

Merci

I'm not sure of the etymology behind "eyepatches..."; however, I've heard the phrase as "putting sunglasses on fire hydrants". And, take it to mean selling something useless, or unnecessary: i.e., selling sand to an arab, or a refrigerator to an eskimo.