It looks like Mechanical Doubling
/ Machine Doubling
. Produces those shelf-like edges. It's not the typical Doubling that could bring a DDO
designation. I started out and had to learn that same issue.
The 'S' mm looks like it is the Trumpet Tail which would make it a FS-511, but it would have to lack the Serifs.
Can't really tell in the pictures if that is the case, but looks like they may be there, just worn. Someone else will have to confirm.
The experts will be along shortly and give you more detailed answers. To the point answers but the correct ones. :-)
HERE IS 'S' MM COMPARISON:
Blowing your Mint Mark up looks like the Serif's are there, but worn, and shadowed a bit with the grime on the coin. So no Trumpet Tail 'S' probably.
Again...I am NOT the final word. Wait for the Pillars and Bedrocks of the Community to show up. We Pebbles are still in training. Lol.