Sacrificial runes are runes placed on humanoids by casters. Sacrifices can be used for the pleasing of deities/patrons, certain spells, or certain items (like the Dark Grimoire). The rune has to be placed on the forehead, and can be used on alive and dead people (but they can't be dead for longer than 24 hours). A dead body with a sacrificial rune doesn't decay at all. A living person with a rune falls into a permanent coma, but doesn't need nutrition. The body gains impenetrable skin, and can't be hurt by things like fire and acid.
You can use the Arcane Mark cantrip to place the rune on a body, but only if the target is dead or unconscious.
The rune can only be removed by the one who placed it, or someone with dominion over that person, like a patron. A body can also only have the sacrificial rune of one person.
If someone is marked with a sacrifice rune, he can't be resurrected. After the body has been used by a sacrifice, the body obliterates. It can then only be brought back by true resurrection.
If you place a rune on a living target, you don't get the XP until that person dies by being used in a sacrifice. XP gained this way is divided by 50.