I have the same wear mark in the same location on my P226 Enhanced Elite 9mm, which I bought about a month ago. Showed up after ~200 rounds.
There's a long post about this on sigforum. My link Some people said it was normal, some said it wasn't. In the end, the OP sent it back to Sig, and they deemed it to be normal.
I'm a little bit aggravated about the wear mark on mine, since it's not a particularly inexpensive gun. But, it's a tool and will be shot regularly, so wear is probably inevitable. I'll keep an eye on it for sure, and will keep it well lubed (Slide Glide).