if that is high build or epoxy you will have a tough time rubbing it off with anything. did they buff the truck? maybe it is dried compound. that stuff is hard to remove also but you can get it off with a stiff brush and soapy water. good luck

1950 custom streetrod build
http://67-72chevytrucks.com/vboard/showthread.php?t=296770

71 corvette conv, 525 hp big block