In the Old Testament in Genesis 4:14-16, it is noted that God placed a mark upon the biblical Cain that would protect him from those that would wish to end him.
Many of the zealous in the Sabbat see this Mark as a religious symbol, a sign of Caine's rebellion against and superiority over God and as such it comes with great faith behind it. During one of the most significant of High Holidays in the Sabbat, the Binding, this ritus may be performed. The one performing this Ritus most meet certain restrictions such as following a spiritual path and having the Mark of Caine upon them already.
The Clergy member leads those before him in a rousing Sermon to Caine and calls forth on from those gathered. That one is chosen by the Clergymen to receive the Mark of Caine upon their brow. It is seen as a defiance and challenge to God's authority as only He should be able to so brand someone and yet the Clergy asserts that they too have that authority.
System: This Mark is etched into the forehead of the recipient in blood derived from a human male. While this is being done, the Clergy must expend 1 permanent Willpower and engages in a static willpower challenge against 10, retesting with Willpower. If successful, the recipient and the Clergy both suffer three aggravated damage that is non-soakable with Fortitude, then they must make a Conviction/Conscience challenge against 5. Should the recipient succeed this test, with Storyteller discretion, they may purchase the merit "Mark of Caine". Should they fail the Conviction/Conscience test, they will suffer a further three aggravated damage.
The Ritus may only be performed during the annual Binding and additionally may only be performed once that evening, regardless of success or failure.