A forum Rank is a little title under your name. If you look over at my profile next to this writing, you will notice it say's "Pattern Flyer" under my name. This is a forum Rank.
Generally forums use a rank system that is tied into the amount of posts you make on their site. I do not see any need to base any kind of tag or rating on a person just by how many posts they have. So rather than setting up a tier of ranks, I would rather let you decide your own.
If you want a title (or rank) for your forum profile, just send me a private message with what you want it to say. Please keep it short, there is not a whole lot of room, but one to a few short words is great.