Mark of Shame
From Halopedia, the Halo wiki
The Mark of Shame is a brand given to those who have either disgraced or turned away from the Covenant. The Mark of Shame is permanently imprinted onto the bare chest of the disgraced being via a special branding iron. After being branded with the Mark of Shame, the being is executed soon thereafter out of sheer humility.
The only known exception to the execution tradition was the Sangheili Thel 'Vadam, formerly the Supreme Commander in charge of the protection of Installation 04. He became the Arbiter and was sent to eliminate the heretical movement led by Sesa 'Refumee over Threshold.
It seems that an Arbiter's name is disregarded and is thus not mentioned due to the disgrace signified by the mark. Ironically, during the Great Schism, the Mark of Shame became a rallying symbol of the Fleet of Retribution and a sign of deference to 'Vadam's honor, often being worn by rank-and-file Sangheili warriors.
List of appearances