There are two things I'd consider in terms of getting a tattoo - and I hate needles, so they'd need quite a lot of persuading.
Oh, and there's a third that would be fun, but there's no way I'd get: the Swedish flag and my regimental patches on the regulation place on my arms. Fun idea, but no way.
Anyway, item one: "In Case Of" tattoo. Name, person number / NI number, nationality, blood type. Just in case I ever find myself unidentifiable... Probably won't ever get this one, but it's one of two I'd consider.
Second option, and one that seems likely I might get: My girlfriend is a classicist, and she also has several tattoos; I don't have any. The ancient Egyptians, though, had an icon called a shenu, and over time we've come to appropriate a sort of glyph based on it. So once a certain question has been asked and answered, we'll both be getting that glyph done. Small - probably about 10mm - and concealable, and with no meaning to anyone who doesn't know the background. That's the way to do it.