I'm sure that they'll have similar markings elsewhere. The underside of the breeching-up ring was another favourite location. Another was the flat area to the rear of the sear axis pin hole.

Incidntally, if you're a Bren Gun fiend and reading this, they feature in the barrel locking nut recess. At one time we had a list of these Enfiield Bren inspectors. I knew one of them, Peter Quick and he commented that '.....after twenty thousand or so..........' I know what he means!