Just implement a system similar to what the game "Foxhole" does?
Every few levels or so every player is awarded a 'commendation point' (so in this case every x number of hours played or something).
At any time for any reason you can give these to another player.
In Foxhole, your account has a level and a rank. Your level is from doing stuff in the game, your rank is largely cosmetic and based entirely on commendation points. (some of the highest ranked people in that game for a while were people driving troops to the front lines).
It could unlock items or like... "tour of duty" stars. Maybe haircuts? I have no idea. Each player can give them for whatever reason they want. The good players would stand out over time.