Renji's tatoos? Why do normal people have em? That's probably the same answer for why Renji has em, but it would be interesting if the writers added some significance to them, like, maybe they're a result of a kidou curse, and because he has them that's the reason why he sucks at kidou. That would definitely be interesting.
My tribal work signifies my "strength" through major events in my life I learn something very important to me, I "immortalize" it.
As for the white headband, if anyone recalls he has lost two sets of sunglasses recently and is known as "Freeloader" around the Urahara Shop. I very much doubt he can afford them.
