Hello,
I have a family member Robert Victor Mayer who has a photo him them in uniform and I am undecided on what kind of uniform it is, being either military or not.

On the cap, there appears to be a downward facing axe and hammer. No insignia on the uniform that I can see other than a number on his collar.

I am thinking the photo was taken in the 1920's maybe the 30's but I think earlier than that. The man in the photo was born 1904.