Pick one that you like and that you won’t mind telling people for the rest of your life.
So probably don’t go with something super obscure because then you’ll seem like a pretentious dickbag (unless it’s something you’ve worked with and then can relate to), but other than that pick whatever one speaks to your soul or whatever.
Carbon is always good for the element of life, and hydrogen is pretty elegant if you frame it right, and ofc there’s always oxygen and nitrogen for relate-ability or a coinage metal for that shiny vibe.
Idk man, it’s your tattoo. Pick something you like. It doesn’t have to be that deep if you don’t want it to be.
First thing that comes to my mind is mercury, for being the only metal that’s liquid at room temperature.
Tattoos can be deep, but they can also just be something kinda neat that you want to have on yourself.