It's an excellent question ….
If the Moderators and Advisory Panel of folks who handle the U.S. rifle forums here. put together a collage of markings and stamps which they authenticate as original, we'd be pleased to create a Knowledge Library entry for on-going reference, as well as "sticky" thread at the top of the appropriate forums.
We do it now extensively for the Enfield and German rifle forums where we have lots of "all correct" examples, but we don't have a lot in the way of authenticated U.S. rifle examples.
Regards,
Badger