As for any in-game mechanics that are supposed to automatically display ones skill: there's Arena, which, to be honest, lolololol, and that's it.
...and as for things such as kill-death, min-loss, etc. Those figures are used in any game similar to Halo to display "skill". But as for in-game, on-engine features, there's lolArena.
Also, the global ranks in Reach do not signify any skill whatsoever. None, none at all. Just experience ("experience" as in what the word defines, not EXP points or anything of any sort).