OP, look for a product called "Liquid Ass" and spray the next sign down with it. You can order it from a popular online retailer. It smells absolutely horrible and the smell lingers a long "ass" time. I would love to see the reaction when they bring that nasty stuff into the car.

Don't get it on your hands. Wear gloves.

Also: "Liquid Ass is made in the USA and never ships from China"