That mark is normal and was no doubt there when you bought it; from factory testing, etc. It has been made on almost every Hand Ejector since 1896 when the first was produced. I say almost because a few model HEs have ctr pins with spring tension to the front instead of to the rear. It's just less obvious on a steel gun until after years of use.

With cyl swung out, put something hard and flat against the center pin (which makes that mark) and push it forward. Verify that it goes in far enough to be flush with the extractor surface. If it does, no worries. If it isn't, stone it flush; it's contacting the recoil shield with undo pressure and gouging the shield.

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Jim
S&WCA #819