I think it's a great idea. I've seen pictures of people who have gotten them to cover up large back surgery scars and to decorate their chest wall after having mastectomies instead of getting implants.

One warning, though, it hurts more to have a tattoo done over scar tissue than over virgin skin. That's what my tattoo artist told me when I went in for a touch up and I mentioned that it stung more than during the original work. It was still bearable though, plus there's more tissue on your forearm than on a shoulder blade to absorb the impact of the needles.

How about a Tree of Life and a crescent moon?