Have done many brake jobs over the years but don’t think I have ever checked for or seen this. Installed new Centric Premium rotors with Akebono pads. Test drove a few miles doing 5-6 medium hard stops from 35 mph. Very smooth and quiet. Looked at rotors and could see a line on both rotors. Not enough to catch your finger but enough to cut through the cross hatching. I’m guessing some dirt or maybe just normal variation in pad surface hardness. Is it work taking part to inspect/clean pads? Thanks.