Skid marks left in the shitter by a man.

1.To Man-Mark, is to use your body, actions and words to purposely impede, confuse and generally sabotage your fellow opponent on the field, during sports play. It s mainly known and used by people in the UK and other countries where soccer/football and/or rugby are popular. However, it is not dissimilar to American basketball players, or hockey players sticking on to certain members of the opposing team, trash talking them, waving their hands and generally being dicks, to distract and/sabotage their intended victim.

This also occurs in social games, like snooker, pool, or darts, when a player hounds another, causing distractions and generally screwing up their chances of successful plays.
2. Man-Marking can also occur during social settings, such as, at a pub, get together, or other social gatherings. for example, a man might linger around his mate, ensuring he doesn't successfully connect with potential dates, or people of importance.

when you have sex with a chick and she wont tell anyone who she banged but everyone really knows it was really you that she did it with and that she got an std from you

When a guy cock slaps a person in the forehead hard enough to leave a bruised impression of a penis on that persons forehead. The bruise must obviously be a penis or its not an official Marked Man.

When a man viciously doesn't let his girlfriend out of his sight, for fear of rival men stealing her away.

You’d normally find mark down in the ENDZ as he says in his chavvy language