On the underside of my penis, I have a V Shaped red/pink patch. It starts about 3/4 down my shaft and gets wider towards the base. At its widest it's about an inch and 1/4 wide when erect. It doesn't itch or burn and there isn't any pain. It is much smoother then the rest of my skin and appears to be slightly thinner. It gets darker when erect or when exposed to hot water. I noticed it about 2 years ago and it hasn't changed a bit. I think it may be a little less sensitive then rest of penis to touch. I used to masterbate in prone position but didn't notice this until 2 years after I stopped.