It's located just outside of my armpit between the pectoral and shoulder muscle. I don't have a digital cam but it looks like an imprint. It looks like when someone bites you and they leave an imprint of their teeth except this one is bigger than teeth markings. Both of my arms have the same sort of marking but varies in size and shape. It doesn't hurt or feel sore or anything. At first I thought it was an imprint from the way I sleep but it's been there for a few days without showing signs of clearing up. I want to goto a doctor to have it checked out but I haven't had the time, plus my doctor is pretty sh!tty. He would probably say it's nothing anyways. What do you guys think? Btw, it's red in color just like when someone bites you. But there is no discoloration anywhere around or near it.