Dont do it. Your car will be demolished 5 minutes after you walk away from it by the mob. Just vote.
Put it (bumper sticker, sign) on a magnetic backing. (Usually available @ craft stores like Hobby Lobby; also may be available as a vent cover @ Home Depot, etc.) Take it off in parking lots, etc.
Or, if really bold, add a 2nd: “If you can read this, you are in range”.