What is the significance of the marker in John Wick's world?

In the John Wick movies, the marker is a small, circular metal medallion that has a great significance in the world of assassins. It is a symbol of a blood oath that binds the holder of the marker and the person who gave it to them. The marker can be redeemed at any time to call in a favor from the person who owes the debt. It is an unbreakable contract that has serious consequences if it is not fulfilled.

The marker is a key plot device in the first two John Wick movies, and is used to set up the conflict in the third. In the first movie, John Wick, a retired hitman, is forced back into the game when his former employer's son steals his car and kills his dog. The person who stole his car is Iosef Tarasov, the son of a powerful Russian crime lord, Viggo Tarasov. Viggo knows that John Wick will come for revenge, so he sends a team of hitmen to kill him. But Viggo also gives John a marker to call in a favor from him in the future if he spares his son's life.

The marker plays a crucial role in the plot of the second movie, where John is forced to honor a marker owed to an Italian crime lord named Santino D'Antonio. The marker represents a blood oath Santino and John made years ago, and when Santino cashes in the marker, John is forced to do a job he doesn't want to do.

In the third movie, John is excommunicated from the assassin community and is given a one-hour head start before a $14 million bounty is placed on his head. He uses his marker to call in a favor from a powerful figure in the criminal underworld named the Director, who gives him safe passage to Casablanca.