What are these "S" stamps on my 03 C stock?

Anyone here know what these stamps are? Stock was made in 1940. I don't recall ever seeing them elsewhere.

Thanks!

https://www.milsurps.com/images/impo...5TerZzrl-1.jpg

What indication do you see that the stock was made in 1940? From what I can see, it is definitely a pre WW2 stock.

what markings are in the stock cut-off recess ?