In settings where there are long established underworld thief, criminal and otherwise ne'er do wells there is going to be a system of heraldry associated with those who live in and rule from the shadows.
There are gangs, there are biker gangs, there are terrorist organizations, and then there are the Sons of Scorpions
Medieval Britons didn't write contracts. Instead, men making agreements would clap their knives onto an altar and recite the agreement three times to seal a deal. Even after the Normans introduced written contracts, British nobles would wrap the parchment around a knife to authenticate it.