Paint scratch filler?
 

I have a black car and used to go to this detail shop that is no longer open and the guy had this black wax (I think it was wax) that he would put on the car after he completed his detail. He would go around and locate minor scratches and even not so minor scratches and put this stuff on it and just buff out with a micro fiber towel. It was neat stuff because the scratches pretty much were not noticeable but after a few days or a week from driving or rain they would show up again. I guess it is some sort of temporary scratch filler and I have no idea what it is.

Any ideas? I am looking to get some.