The reference was more to show how most pistol markings were applied. On the 1911A1 the slide and receiver markings were put on with a roll die, but the acceptance marks were hand stamped, and are normally crooked in that the die was not sitting evenly on the steel when struck.
Some 1911 slides are know with the roll mark on the opposite side, apparently where the operator got the slide turned wrong when the roll marking was applied.