Likely the remnants of a barrel mounted sling loop…….about the right position.

Bores look decent, good Henry rifling, should shoot!
Engraving has not been unduly softened by past buffing, looks like you got a good one.
Can't really tell from the one picture, the firing pin (striker) head appears kind of flattened? Maybe peened by excessive dry firing over the years. You will know for sure if/when you try to remove it. Easy fix.
- Mike