Just throwing some more food for thought and up for discussion/debate. I’m not 100% convinced on a lot of things regarding this stigma. That being said, I have more faith in Chumak’s group than any other source at this time. Depending on the era and platform, I’ve seen it unofficially ID’d as all sorts of different things. For example, some Nagant’s will have this stigma and some will argue it’s a state inspector manufacturing for quality frames, while others will say it’s a repair marking related to firing issues. Then the marking can be by itself or within a square. IMO if it were related to just quality frames, we would expect to see it on all Nagant’s when initially inspected at the factory. Then the argument of how significant the repair was could possibly dictate whether the marking stands alone or enclosed within a square. This marking, whether alone, within a circle or within a square can be observed on several different platforms from as early as the 1920s well into the 1970s at least. A few examples are the Nagant, TT, PPP, PPS, MN, PM, SKS, AK, and several others.
Here are a few examples of the Nagant for reference and note the marking is not always in the same location.
Solo П:
Solo П: 1921 repair:
Circled П:
П squared, no other repair markings:
П squared, multiple repairs:
To further convolute the matter, some have ID’d the early marking within a circle as being a test stigma for the strength of weapons test cartridges and two circle rings as checking the strength of weapons designed to fire “Magnum” cartridges.
So, the water in my view is still murky but is it possibly the marking means a few different things (frame inspection, firing related repair, test stigma, etc)? IMO no, markings that remain the same over long periods of time don't drastically change (overall general intent of the marking). Obviously some deviations and variations is very plausible but I would think they are all generally related. IMO though, if the П is enclosed in a square, I think it’s relatively safe to conclude it was part of a repair. Of course I could be completely wrong but from what I've seen to date, it is extremely likely the case.