I can't really take a pic because I'm currently using it and I doubt my camera would pick it up but I haven't had any problems. I actually was just running some stress tests and my temps are fine. Lets just say it looks like a dirt spot and it feels smooth when you slide your finger across it. It's pretty centered and I had noticed it when cleaning it. If I were to slide the tip of my nail across it you would somewhat feel it. Also, I cleaned it with q-tips, rubbing alcohol and coffee filters.