It is only idolatry when you worship the symbol itself. Using a symbol to identify yourself as one who worships Christ is not idolatry.
SnakeDoc
When I was younger, the man in the Catholic family next door got a full upper arm tattoo of the Virgin Mary. This thing was extremely intricate, full-color, and cost him $800 over 30 years ago. I can still remember how beautiful it was. That it was still glistening with the Vaseline cover added to the effect.
People can argue propriety and idolatry all day long. All I know is the creation of his tattoo brought some more beauty into the world, and that can’t be be all that bad of a thing to do.