Well jond,
We can now see you have a Milled type III (some call type IIII) Straight hammer.
A Marking I've never seen before, some Post WWII were unmarked but.........
Have you taken it completely off to see if there are markings on either of the bottom sides ?
One thing for sure.. you clearly have a odd stamping.

I'll show your pic and ask some others on different forums.

BTW- Curious about the maker of your Carbine, I don't believe you said who made it.
Also curious about the maker of your Trigger housing. Looks to be a Type III milled with the square rear lugs.
I can see just the S on the upper right rear...... Is there any number on the left side we aren't seeing ?

Hmmmmm....