Traveller's smile
The sign of someone who's fought a traveller. A scar caused by a pair of razorblades or Stanley knife blades concealed within a piece of cardboard. Since the skin tightens when cut, the two blades cause a nasty scar which sometimes never heals. It is often done down both sides of the face, so it forms a "smile" shape, hence the name.
Oh, my god. That guy's got a traveller's smile