I have a cross on my left upper arm with words "John 3:16". I also have a Celtic, or Irish, cross on my right upper arm. Both can't be seen with regular short sleeves. My next one will be on my lower arm, so I have to be careful choosing it, because it will be seen. I'm thinking about an Amercian flag, or some other patriotic symbol.
We have member of our local board who actually has an IAABO emblem tattooed on his upper arm. Now that's loyalty.