If I ever got a tattoo (unlikely!), it would probably be an ensō. This is a symbol important in Zen Buddhism and Japanese ink painting.

The circle is drawn quickly and fluidly, in a single stroke.

“Once it’s drawn, there is no changing it. … the circle signifies unity and completion. Perfect balance. What makes the ensō more intriguing is that it is not perfect at all. It is rough, messy, and at times not even complete.” [Aly Juma]