Mark of Shame
From Halopedia, the Halo wiki
Summary
The Mark of Shame is given to those who have either disgraced or turned away from the Covenant Empire (in other words, Heresy). After being branded with it, the person is executed soon thereafter. The exception was the Commander in charge of the protection of Installation 04. He became the Arbiter in order to settle the act of Heresy on Threshold. The Mark of Shame is imprinted permanently on the body of the person by means of branding. The Mark is available as a Halo 2 Multiplayer Emblem.