Ahh you are correct Ryu, let me explain, Frankie stated at ComicCon with the lead of the War Gsmes, that there is going to be a 1-50 'esque' system, it may not be numbers, it may be symbols or titles, etc. but there will be a system that in some sort of way can be associated with the old school 1-50 system of Halo 3. He also stated that only you the player can see your own Rank.
I should have clarified about the xp/Sp differences, you are also correct Ryu that as you play you gain Xp, similar to cR from Reach. and as you level up you earn Spartan Points to put towards weapons, armor, skins, loadouts etc.