Sword of Omen is a one-hand sword that is most often sought after by Rogues.
This item is a reward from the Horde quest which starts with Varimathras in The Undercity. To complete the quest, you must slay Herod, High Inquisitor Whitemane, Houndmaster Loksey and Scarlet Commander Mograine.
The Sword of Omen is a reference to the popular 80s cartoon Thundercats. The icon for the sword closely resembles the sword from the cartoon, though the in game rendering of the sword does not.