Baylor University in the USA, in collaboration with Texas Tech University, has been carrying out research into faith-based and religious tattoos.
They've made some interesting findings. Analyzing hundreds of photos of Christian students' ink, it was found that tattoos with deep religious significance for the wearer are more likely to face inward positioned inside the wrist, for example because they are usually a personal reminder of values to live by, rather than a public proclamation of belief.