The Samurai tattooed themselves to signify they belonged to an elite organization that served.
The Inuit ,and some Plains tribes tattooed their faces as decoration, and too establish their singularity in tribes that called themselves"The Human Beings"
Different Gangs will tattoo their marks upon their body as a signature ,and proud display of their belonging.
Vikings tattooed themselves because it was in their culture to endure pain, and show how they will belong in Valhalla.
Decorating your body with piercings, scars, or markings that are permanent has been done since before recorded history. Some believe it is a part of our genetic memories.
It gave,..and gives us, a sense of belonging to a group, as well as individualizing ourselves.
Only human beings create art, for the sake of creating an individualized monument, even if it's upon our own skin.