Mark of Indenture

A Mark of Indenture was a memetic marker which confirmed a deal between the Celestis and members of the "lesser species". Everyone marked by the Celestis became a servant of them upon death. (PROSE: The Book of the War)

The Eighth Doctor was able to avoid being marked by the Celestis by having a Shift trapped in his mind; when Trask attempted to mark the Doctor, he missed and marked the Shift instead. Kristopher Patrick Englund received the Mark in exchange for guaranteed survival of his surgery. (PROSE: Alien Bodies)

While The Brakespeare was outside the Spiral Politic, Lord Dervishage didn't have to follow the rules of the Politic and thus didn't require a Mark of Indenture to take on an individual as a servant. Dervishage took control of everyone that died on The Brakespeare, forming his own empire of the dead. (PROSE: The Brakespeare Voyage)