Travel to the tattoo artist and do his task. It involves one of each archon token, and possibly a crystal egg. The mob you need to kill damages you based on a system of calling marks. If he calls a mark you don't have, you die quicker.
For taking command of a potentially dangerous situation, the Powers have granted thee a Mark. You have been granted the Mark of Command! You gain 216 practices! You gain 648 quest points!