S and BERN on the damascus barrels, right barrel have the E in BERN back to front
I think its the stamp of the barrel maker

"BERN" most likely stands for A. Bernard, Liege, Belgium, who in 1855 patented a novel, improved damascus pattern, named for him "Bernard Damast". Most high grade damascus Barrels were imported in the rough from Belgium, where they were pattern welded by many specialzed smithes in villages around Liege. Rough damascus barrels were marked by the smithes as to pattern, as the figuring only becomes visible on finishing.