Dude, I write on my hands (and occasionally arms) all the time. I don't know what NT's are like wherever you are, but nobody where I have lived has ever had a problem with it. Heck, they do it too. All the time. I repeat: NT's do it too. It's not that unusual. I got in trouble for it in science a couple times because apparently, "my cells don't like it." not because it's a social don't or whatever.