Markers are a blood oath between two individuals. Markers are also formally witnessed or recognized; It is not just any blood oath.
When John Wick wanted to leave the assassin life behind to marry Helen, he was first assigned an “impossible task. by his then employer Viggo Tarasov. In order to succeed, he gives a blood oath to Santino D’Antonio, the influential son of and later brother of one of the 12 members of The High Table, in return for his aid. (At the time the marker was given, D'Antonio senior, the art collector, was the representative for the Camorra at the High Table.)
After John came back from retirement to seek vengeance on Viggo and his son Iosef, Santino calls in the oath. Desiring to take his sister's place at the table, D’Antonio has John Wick assassinate her to satisfy his commitment. Afterward, Winston compels D'Antonio to acknowledge the Marker's fulfillment.
A marker is a small round metal object indicating the debt of a blood oath between two individuals. Opening in the middle to reveal a divided surface, the debtor presses a bloody thumbprint on one side to commit an oath is owed, while the borrower likewise presses their bloody thumb to the other side to indicate when an oath has been fulfilled.
- The Latin words "Quod Debitum Sanguine" carved on blood markers means "blood debt".