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So, either stencils and a serial/product code, or stencils and a combination of first inital of last name, and last 4 SS digits...

Those sound viable, I'd lean towards the second

Likewise, good Obie. I cannot avoid a puzzle.

I like that. The M denoting size, and the rest being an issue number. That makes sense.

Cheers,
Jeremy

Good point, Obie... Maybe the military had letter and number stamps and you stamped your own? No.. That would take too much time...

Maybe they were ISSUED by the military, stamped for each person?...

I think we have a winner