The stor of the arbiter. ok if I remeber right, he was a commander in one of covenant armada. I cant remember what it was that he failed to do but anyway the prophets gave him the title of Arbiter. Now in Sanghelios culture (sangheli is the name of the Elites) one regains his honor by dying in battle. So in a simplified version, thats how the arbiter came about.
The guy asked where the Arbiter got the mark shame not his story. If I remember correctly it was on his chest.