What markings will tell you if an upper was made by RRA? Or does someone else make their A2 uppers?

Are you asking about lettering on their forgings?  Very few companies (if any) operate their own forges...they have their own forgings at the forging houses (of which there really aren't too many)in which their receivers are made, and then do/have done their machining, pre-finishing treatments, finishing, final assembly, etc...
There have been a few postings over the past few years with the markings/designations for most of the military markings, but I don't think I've seen one for the civilian markings.
Sluggo