That may not even be Damascus. It could be a pattern put on the gun to make it look Damascus. In those days, the Damascus gun had a better reputation than the fluid steel barrels of the day...
Hmmm...
Now, that would make a lot of sense. How in the world could a Damascus craftsman repeatedly incorporate letters into his process. I'd think that would be just about impossible. Wonder how they put that pattern in place such that it would last?