I'm not a big fan of tats, personally. Nothing against anyone who is covered in them, it's just not for me. Though I am heavily thinking about getting one at some point. As such, it'd have to be something heavily meaningful.

Here's what I've come up with, to incorporate both my Scottish heritage, and my Christian beliefs:

The standard belt/buckle of the clan mottos. The text reading "Diem Premier Servi" which I've read somewhere is a motto of MacEwen, therefore pulling in both the Scottish side, and the Christian side too. Inside the belt, I'm thinking something like a lion with a crown of thorns on its head. Maybe a cross in the background as well. I haven't figured it out completely yet.

Something like that though, or at least something else equally symbolic.