When I was in high school, I wrote a TI-86 program in BASIC to do geography/physics formulae. Like “find the volume of a cube” and then it would ask you for the variables and solve for whichever one was missing.
My teachers found out and actually ruled it not cheating because I wrote the program myself and hadn’t shared it with everyone. (I eventually became a computer programmer so she was probably right.)
So, I’d say by that precedent, as long as you gave yourself the tattoo and learned a new trade, it’s fine. But looking at a friend’s tattoo would be cheating.