I picked up a nice little model 12 the other day with an octagonal barrel and a serial number that indicates it was made in 1927 (719XXX).
With the octagonal barrel and manufacturing date, I expected it to be a 12C, but it just says model 12 on the receiver above the serial and no where else on the gun is there anything that points to it being a 12C.
So it makes me wonder if 12C markings on the rifles were common, or we were just expected to know which iteration of the model we have...or maybe it has nothing to do with it, for I know I had poked around the internet and I saw some model 12s with straight stocks, some with heeled stocks, some with round barrels, some with octagonal, some apparently only shot shorts, some didn't, to the point I was confused about what I have, or even if they designated different iterations.
BTW, the serial number is also inside the receiver housing attached to the stock.
Jim