I (sigh) have had to buff out the SL front bumpers regularly...my wife seems to have a bit of trouble maneuvering the front end around when negotiating the garage or gate entrance...so either she takes the paint off the garage threshold, or the paint from the wrought iron!
Since most of these swipes are at slow speed and generally corrective steering occurs before the bumper gets too intimate with the object being encountered, the resulting paint marks don't get a chance to "burn" into the finish.
So as John Plut aptly stated, polishing compund will do the trick. Rubbing compound will remove the most stubborn of these, but it's more abrasive and will make the treated area hazy. So you need to follow up with polishing compound and a good wax.