It seems that the holy stigmatists are of some relevance here: Padre Pio and St. Francis, to name the most popular.Also, the Copts.And this was particularly helpful for me: http://www.catholicnewsagency.com/cw/post.php?id=569
God knits us together in the womb. Like snowflakes we are similar yet unique. I do not think that a tattoo improves on the individuality that is ours through the natural process of being conceived and born of woman. I think of tattoos the same way a curator would view graffitti on a masterpiece.