It is just signs that let you know it has been either backed into some, which is common and likely the case. Or the other thing is somebody slap (tap) that back in a parking space (lot).
Not really noticeable so they drive off and seen most people dont do a walk around or back in then it would get much notice. I use to live in DC ever car there that parks on the street gets bumper every day. Now I live in FL so you have the old and the young to worry about. So when people there car never been a accident unless you know them, then they are probably blowing smoke!
