Ink.

Okay, you're at the South Pole. It's 40 below. 
The polar bears are jogging to keep warm.  In fact, they've jogged all the way from the north pole, their normal habitat (Hey, I check this stuff before I post it.)


You're a detective, on the trail of a sadistic serial killer who is posing as a penguin hunter in the lowest of latitudes.  Your only clue is the fact that he has a pair of distinctive tattoos:  A grey wolf on his shoulder and a condor on his upper thigh.  How do you find him?

Easy.  The bastard will be wearing shorts and a sleeveless shirt.

You don't get a tattoo because you like the idea of some hairy biker squirting Chinese printing ink under your skin; you get it because you want people to SEE it.

You know what would be really cool and 'out there?'  INTERNAL tattoos.  A remote control needle inserted into your lower latitudes.  "Mom" written on the top of your spleen.  How about a full sleeve tattoo on the inside of your arm?   Or a tramp stamp that will only ever be seen by a proctologist?

In fifty year's time the orderlies in the nursing home will be laughing their asses off when they're giving Conor McGregor a sponge bath.
"Hey, Mr. Mac, what's that thing on your chest?  Kinda looks like a dried-out aubergine with a splash of ketchup on in."
"It's a futtin' gorilla with a futtin' crown on his head and a futtin' heart in his mout'"
"And this one, on your wrinkly old arm, what does it say?  Something about a moose?"
"It's the futtin' Navy Seals motto. Slow is smooth, smooth is fast."
"And that's a leopard on your belly?"
"It's a futtin' tiger."
"Right.  It's just, the moles kinda look like spots."