Rubber marks on a bumper are caused when the vehicle hits another vehicle, or rubs against something inadvertently. They are also caused by shopping carts hitting the bumper. These marks typically occur only on painted bumpers, not older metal ones and are actually just rubber deposits left by the other object. Since the marks are really nothing more than a surface stain, they can be removed with basic automotive detailing supplies.
Rub your fingernail over the surface of the rubber mark to determine if any of it scratches off. If none of it comes off, then it is most likely a scratch, and a professional must repair the paint.
Wet a piece of 1,500- to 2,000-grit sandpaper until it is completely saturated and the surface appears dark. This sandpaper is now more of a buffer than a sander and feels extremely smooth to the touch.
Place the wet sandpaper on top of the rubber mark on the bumper and move it in a circular motion until all of the rubber marks are gone.
Wet a sponge and squeeze it out to remove most of the moisture. Apply 1/2 tsp. of polishing compound to the sponge.
Place the sponge onto the area where you removed the scratch and move it in circular motions to buff the area and remove any surface scratches.
Rinse the sponge in clean water to remove the polishing compound. Squeeze it out and wipe the bumper to remove the compound residue from it.
Wipe the area dry with a lint-free cloth. Then, apply 1 tsp. of car wax to a clean, dry lint-free towel and apply it to the area until it is no longer visible.
