I need a good spot for a tattoo that can be hidden from parents. the tattoo will be a "13"?

A guy in a town near me is doing a special deal today. It's 13 bucks for a 13 on friday the thirteenth. I've always looooved the number 13, and this is my perfect chance to show it. However, im only 16, and my parents dont approve of my getting tattoos. Even though i already have one on my hip, which will be hard enough to hide. So, i want the number thirteen, but im not sure where. I was thinking behind my ear, or a small one on my wrist. Suggestions? Thanks!