Never!
Hmmm…a stylized rainbow might be nice. Upper left arm. Hey, OP, you should have asked where I’m not going to get it!
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My logo, but I’m not sure where I’d put it. Bicep, back of my head, entire back? I dunno.
I’ll never get a tattoo, because it would mar my beautiful body, but if I did, it would be script like this is not a tattoo along a limb.
I like birds and I like ravens in particular. So IF I was ever to get a tattoo (and at this point I have no such intentions) a raven would be likely.
Probably some version of the Wheel of Fortune from Carmina Burana, complete with the “Regno/Regnavi/Sum Sine Regno/Regnabo” labels
Or I might just take a page from Rapid Roy the Stockcar Boy’s book and get a tattoo that just say “Hey”.
That’s pretty cool, but Rapid Roy actually has two. The first one says “baby”.
No Mohr’s Circle? I always thought they looked cool.
If I wanted something to match what I actually ended up doing, it would match my icon.
Well, I’m an electrical engineer, not mechanical, so Euler’s identity is closer to my heart.
Understood.
For me, the Mohr’s Circle is attached to an epiphany I had in college. When we were learning about 3-d stress, we first learned the raw calculations. Every homework problem took 3 to 4 pages. Then we learned the Mohr’s Circles and the homework was much easier.
After we had turned in our second set of homework with Mohr’s Circles, I asked: “When we’re working as engineers, will we be allowed to use the circles, or will we have to use the equations.”
The answer: “Neither. You’ll look up the answer in a table.”
The U.K. flag
It would likely be a cat tattoo. This one is a good option. I have seen a couple of others I like, too.
It would probably involve a significant amount of alcohol and a very short space of time but:
“I told you no foockin’ tattoo here”
Fifteen years ago or so, I briefly considering getting a tattoo on my upper arm. I never did, but I would have gone with either a 20-sided die, to reflect my primary hobby of role-playing games:
…or the Rebel Alliance symbol from Star Wars, to reflect my favorite films:
If you have no intention of having a limb amputated, which one would you amputate?
That one.
I would get a band around my arm, a musical staff, featuring the 1st 4 notes from Mozart’s 41st Symphony, 4th movement.
I know, but a tattoo that says “baby” is tacky. One that says "hey " is cool.
It would be this (look closely): .
It would be at the nape of my neck and covered by my hair. If it was somehow spotted, it would be so small that it would be mistaken for something natural.
A tree, with roots. Live animals in the branches of the tree, some of them eating its fruit and leaves; dead ones in the roots, feeding the tree via fungal connections.
Still not getting one, though.
So, a mole? 
Ewww! LOL