I think they are listed in the present thread's first or second page (ok, maybe third) ....
These ranks correspond to your postcount , a bit like the user text if you don't change it ... They differ according to your role : forum member (regular army), moderator (military police), or Sentry Studios team (special ops) ... They have been made by the great photoshop artist ElectricSheep, and were introduced here by DarkBls... Erh, what else, well, they are not implemented right now, and several people really dislike them (hence the "**** the ranks" insigna in their signature) .
I think that's it.
Edit : no, having checked, they're not in here. But there :
The original thread (sorry DarkBls)