Go to the towne of Rune judge and visit him, then go to the the towne of Xaventry judge and visit him (hes in a hidden west exit in the Lady Undya Chambers), then go to Templeton and visit the two judges there (Strom first, then Powers). Then head to Maldra Keep and visit Judgment in the tarot section. After you have done all of this, you should receive the mark.
For exhibiting an interest in legal matters, the Powers have granted thee a Mark. You have been granted The Mark of Arbitration! You gain 44 practices!