Arrow in the triangle stamp on the front trunion of a Saiga

I have 6 different Saigas. 2 Saiga 12, 2 Saiga .308, and 2 Saiga 7.62X.39.
None of them have the Arrow in the Triangle stamp on the front trunion.
My buddy just bought a Saiga .410 yesterday. His front trunion IS stamped with the arrow in the triangle on the front trunion. Are all of the .410 Sagais front trunions stamped with the Arrow in the Triangle? Or is his just a fluke? Are any of the other Saigas being stamped on the front trunion with this mark? Just thought it was cool. They are stamped like my PLO kit. Thanks, glocklon