Usually used as a degrading punishment to slaves ex: making them write cum slut, whore, ect in prominent places on their bodies. Usually photographed and placed online as part of punishment.
Also can be used as a way of laying ownership to a slave.
My master is into graphoerotica and has ordered me to write cum slut on my face.
The slave has "slap me" on her breasts as part of her graphoerotica punishment.