It's one of his dog tags. I took a cue out of the movie "Sniper" and put one of his two tags on his boot. That way, should he be blown apart, they can tell who he is. Or so the story goes anyhow.

If you like that story, research why there's a notch in the original dogtags. About the boots. The instep and outstep (is that a word?) look about the same, which kind of results in the clown shoe look.