Tattoos

They're popular among most Zells, and human sailors often emulate this for good luck. It's also considered very pious to get a tattoo of a stylized sun somewhere on one's body among Genosians, since it's very painful and labor-intensive.
Dessians also do it, but more for aesthetic reasons, and they're more likely to get tattoos that people actually see.
Dace in general views tattoos very negatively, because they were often tattooed during their time as slaves. The Orredin couldn't be bothered to recognize their faces, and so tattooed obvious ques as to their jobs on their faces, so that they could be quickly identified and ordered about.
Karthacks frequently have moon-themed tattoos if they are associated with the clergy, and the Zophs are fond of basically tattooing reference guides to their personal sorceries on their arms in code. In a bit of irony, a great many Genosians mistake these tattoos as symbols of strength, virility, etc, and emulate them. There are Lagorian and even Reichlanders walking around with utterly priceless secret sorceries written on their arms, copied off of drunken Zophs they met while at war, and then tattooed on themselves.
These days, the only inkwork that is sanctioned in Dace,is the mandatory practice of tattooing the "humor type" of a soldier on his arm, just above the bicep. That way the surgeons know what to do with him if he is injured. This has become a sort of badge of honor among veterans.
Dwarves also make great use of tattoos, particularly to identify friends of their clan. Humans who are Dwarf-Friends are often given intricate tattoos that identify them to other dwarves, allowing them to access and trade with various Holds. Dwarvish "inkweavers" are widely considered the best in the world, even by Zells, who invented the art.
Rade Sark decided that tattoos were degenerate, so he outlawed them among his people. He has several himself, but he hides them beneath his uniform to avoid them being seen.
However, Zells place a high emphasis on visual ques of status, so he first developed uniforms to convey rank, and then grudgingly condoned the veneration of scars and other war trophies among his men.