http://www.yalibnan.com/2009/12/27/ashura-ceremony-in-lebanon-in-pictures/
It is very likely he received this scar when he was Muslim when he was in Indonesia. His stepfather most likely insisted on it. It is an actual ceremony where the young males will have their heads cut open with a sword or large knife. Sadly, this is the most plausible theory I seen thrown around.
Well, his mother DID send him away from his step father, to live with his grandparents, before she divorced her husband. I bet he had some good beatings in Indonesia.