Master Sergeant

These titles were only obtainable in Vanilla (pre-BC). You would obtain a higher title as you got more PvP Kills.

There -were- 14 ranks in all (Blizzard has announced that they're bringing back PvP Titles in Cataclysm. Maybe some similar to these pre-BC ones.)

(Quoted from World of Warcraft PvP Ranks)

1 Private (Scout) - Allowed purchase of Private's Tabard
2 Corporal (Grunt) - Allowed purchase of Faction Insignia
3 Sergeant (Sergeant) - Allowed purchase of superior (blue) cloaks; 10% faction price discount
4 Master Sergeant (Senior Sergeant) - Allowed purchase of superior (blue) neckpieces
5 Sergeant Major (First Sergeant) - Allowed purchase of superior (blue) bracers
6 Knight (Stone Guard) - Access to Champion's Hall (Hall of Legends)
7 Knight-Lieutenant (Blood Guard) - Allowed purchase of superior (blue) boots and gloves
8 Knight-Captain (Legionnaire) - Allowed purchase of superior (blue) chestpiece and leggings
9 Knight-Champion (Centurion) - Allowed purchase of Battle Standard
10 Lieutenant Commander (Champion) - Allowed purchase of superior (blue) helm and shoulderpads
11 Commander (Lieutenant General) - Allowed purchase of PvP Mounts
12 Marshal (General) - Allowed purchase of epic (purple) gloves, leggings, and boots
13 Field Marshal (Warlord) - Allowed purchase of epic (purple) helm, shoulderpads, and chestpiece
14 Grand Marshal (High Warlord) - Allowed purchase of epic (purple) weapons and shields

Luckily, anyone who got their title before they were inactive got to keep it, and it became a "Feat of Strength" achievement.

They didn't take a set number of kills, except for the lowest ranks. Private through Sergeant required a certain number of kills, but everything beyond that was competitive. Grand Marshal, for example, was awarded to the Alliance character who earned the most honor during the previous week. There would only be one Grand Marshal at a time, and if the current grand marshal decided to let their rank lapse (most would, just because it took truly absurd amounts of grinding to earn the rank), they'd drop back down through the ranks.

Used to be the highest rank that had no competition in the old honor system; meaning, after this rank you were fighting other people on your server for said rank. Private-Master Seargent were not "officers" and did not compete.

Both my warrior and warlock have this same rank, it's not exactly Grand Marshal, but its still pretty cool as its so rare (most who bothered going that far kept going to get Marshal or even G Marshal). Fun stuff

*Misses the old honor system*