
1) Automotive accessory 2) Moving message 3) Promotional freebie
Found on
https://www.crosswordclues.com/clue/bumper-sticker

A bumper sticker is an adhesive label or sticker with a message, intended to be attached to the bumper of an automobile and to be read by the occupants of other vehicles—although they are often stuck onto other objects. Most bumper stickers are about 30 cm by 8 cm (12 in by 3 in) and are often made of PVC. ==Purpose== Bumper stickers can be comm...
Found on
http://en.wikipedia.org/wiki/Bumper_sticker

an adhesive-backed strip of paper for sticking onto the rear bumper of an automobile, usually bearing a tourist advertisement, slogan, joke, etc.
Found on
https://www.infoplease.com/dictionary/bumper-sticker
No exact match found.