This mark was acquired by Alfo after he made a deal with an orc warlock, for a magical item.
So far, it appears to be transmitted through touch.
It has spread throughout Sindaleth quite rapidly even marking Elidyr Ashebow.
The mark appears to be trackable.
In the end, the mark proved to be not only a way to view Alfo’s actions, but a way to enforce his promise to Duraz, the Orc Warchief.