These rear window "Caution" suction signs help to identify Rural Carriers as postal vehicles. The USPS vehicle signs simply suction to the rear window and can easily be removed when the vehicle is not being used for USPS deliveries. The suction cup adheres best to a clean and dry surface. Signs features a yellow polythylene and opaque plastic construction with black screened lettering and measure 5 1/4" x 5 1/4". Ships USPS.