okay so i'm really late on this, but here আপনি go. IT IS A BITE MARK. anyone who knows anything about paula, knows she is a psychopathic freak. আরো than likely, it was from her. a hickey, people, is visable as one large spot on the neck. there are several small teeth marks on 2D's neck. and that's that.
Clearly a hickey. Remember, right before they started working on Demon Days, 2D was a bit of a manwhore and now has several illegitimate children (I wonder if he knows they exist??) But I DO NOT think Murdoc gave it to him. I don't think Murdoc is attracted to 2D.