It could be struck through cloth? Part of a mint workers uniform? Did they have uniforms in the 40's at the mint? Or were they allowed to wear regular work clothes? Looks a little like a lamination. Something is going on there. Not PMD.
That would actually have more of a blurry appearance to the area where the cloth was covering. The pattern of the fabric will show also.
I should have stayed with my first idea. Which was lamination/ de lamination. But then I thought I saw some texture/cloth pattern to the area.