You are correct about the markings: if you look up the import section of the 1968 GCA, there are regulations involving the marking of firearms that are imported into the US. The importer's name, city, and state of business are the first part of the marking; the second part is the country of origin (or perhaps manufacture, I haven't looked at these for a long time since the most desirable examples just don't have them).
The interesting aspect to all this is the arbitrary decisions by the ATF about what must be marked and how. Early examples would be marked very discreetly, such as under the stock or with small stamps on the underside the barrel near the muzzle. They decided this wasn't good enough, so I think now it has to be on the receiver itself, which is how you get ugly things like the most recent batches of Swiss K-31 and K-11 rifles with 3 lines of electropencil text across the beautiful classic blued curves of the top of the receiver.
My guess, which could be confirmed by looking up info on the Blue Sky import M-1 carbines and rifles, is that arms that originated in the United States may not need the country from which they were imported stamped (or may not have in the past).
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