I work a lot with very dilute solutions, so I got the equation for calculating Parts Per Billion on my arm. The mods actually host it on this site, the link is at the bottom of the page right above the modlog
It's a tattoo of Ceanothus americanus, from a botanical survey of North America commissioned by the first continental congress in 1774. The lettered images on the bottom show the development of the flower head and seeds.
Ohh I am in the process of convincing my wife to let me get my light cone tattooed on my arm. Just a small flat versions. Nothing super fancy I just like to envision a tattoos that is relative to me.
I have other dumb ones from when I was younger but they're not who I am now.
But my time cone the dot being my present and the cones a reminder of where I have come and where I am going, along with the limitations of the universe