It's what you see here directly below and it front of the slide stop.
It's easy to get frustrated when replacing the slide stop after breaking down your 1911. It takes practice.
The round scratch you see can never be buffed out and is evidence that the owner would have tried ANYTHING to get that little booger back in place.
Don't make the same mistake, you will be sad for the entire time you own the gun. Take it SLOW AND EASY when replacing the slide stop, no matter how frustrated you get.