OM Blackhawk Cylinder Question

[SBHRSSSSS]

On a couple of OM Blackhawks, I've noticed a stamped letter in the front face of the cylinders. Are these stamped letters of any significance? What do they indicate? Thanks for your help.

 

[rugerguy]

the stamped "S" meant it was proof test and or hardness test, what ever, it is a "final " inspection stamp.
other markings, or numbers are meant for the "spare" ( extra) cylinder for the convertible models......

 

[contender]

Dan is correct, as usual. The stamped letter, a proof mark. The electric pencil etched numbers, usually 3 of them, are the last 3 numbers of a serial for the spare cylinder. keeps the guns together when assembling them at the factory, AND for those of us who have more then one convertible.