Sword of Omen

Sword of Omen is a one-hand sword that is most often sought after by Rogues.

Source
This item is a reward from the Horde quest Into The Scarlet Monastery which starts with Varimathras in The Undercity. To complete the quest, you must slay Herod, High Inquisitor Whitemane, Houndmaster Loksey and Scarlet Commander Mograine.

Trivia
This sword shares a name with the weapon wielded by the main character in ThunderCats.