- This Mailbox Address decal is up to 4” high x up to 10-1/2” wide, depending on address length. - 5 CHARACTER LIMIT **Please include the numbers for the address in the Personalization Box ** This Mailbox Address Decal is cut from Genuine 3M, Automotive Grade, Retro Reflective Safety Vinyl. This is the same reflective decal material used on police cars and fire trucks. They look like regular decals in the daylight, but at night they glow under flashlights and headlights.