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
Except, it doesn't have to be. Nighttime can be a relaxing, peaceful time in the world, when nature rests and soft shadows cover the ground. Not every night has to be filled with vampires, ghosts, beasts, and things jumping out from dark places.