Under the trigger guard near the safety there is a little notch. I'm not sure if it has any other purpose besides pinching your finger. I've sanded these spots down on all my USP's and I'll bet the person that owned your pistol before you did the same. When I have done this, the area is a little lighter than the rest of the frame. I suppose you could refinish your whole frame-but as you carry and shoot it wear marks will appear, it will get scratched, etc.