Rhys’s tattoo is on both knees : twin tattoos of a mountain with three stars above it. One mention in the books describes them as “twin tattoos on each of his knees,” and a fan discussion notes the symbolism as bowing to nothing and no one but his crown and Feyre.

Book Detail

The tattoo is described as subtle but striking, not on his hands or arms. The same source places the first mention in A Court of Mist and Fury.

Symbolism

Readers commonly read the mountain-and-stars design as a sign of defiance and loyalty. It fits Rhys’s character as someone who answers to very few people.

Note on confusion

Some online posts mix up Rhys’s tattoos with Feyre’s bargain tattoos, which are described as being on her left arm/hand with an eye on the palm. If you meant the bargain tattoo on Feyre , that one is on her left arm and palm, not on Rhys.