Contributing to this whole Saint Christopher medal discussion, that had me curious, so doing a bit of "Bones" past episode research, this is the best look of Booth's medal that I could get:
(Screencap by Bones Daily).
Well, it's not his medal exactly, it's the one he gave to Jared, in "The Beaver in the Otter", however, it seems it's just like Booth's (considering Jared thought it
was Booth's at first, and from other glimpses we've had of Booth's medal, definitely looks like an exact match).
I then made a crop of the medal Brennan is wearing for comparison:
And while I hate to rain on anyone's parade, they really don't look like a match to me. However, I'd be quite happy if I was wrong, and it's possible that is some sort of Saint Christopher or religious medal, maybe just not Booth's exactly.