You're probably right. Interestingly enough, the <ГИС> stamp is pretty old, I've seen it on stuff that dates from Soviet breakup times.
Another stamp I've seen before and know is relatively old is the "micrometer symbol"...maybe a "PCT" abbreviation. You see it on stuff all the time, even to this day:
the <ГИС> stamp is some kind of State Test Station certification...it's been in use for a good while, most weapons and ammo boxes have it. I "think" I have even seen it as an ammo headstamp. I'll have to dig into and probably through the heap and see what I can find..
The "PCT" stamp is on all Saigas, and probably others.. both my Saiga 12 and 410 have it. It's a Patent Certification symbol, look on most weapons and ammo boxes.
Both my Russian Makarovs have it......so the "PCT" stamp has been kicking around a while as well.