Seal of the Dawn

The Seal of the Dawn is a trinket that serves as an and increases attack power against undead enemies. As of the Cataclysm, the quests for earning it are no longer available, so new players cannot acquire it. However, players who completed the quests prior to the Cataclysm can still get a replacement if it has been destroyed. They can also acquire instead.

As stated, wearing it will cause undead mobs in the Plaguelands (and their dungeons) to drop scourgestones; however, these items no longer serve any purpose.

Source
This trinket is available from Betina Bigglezink at Light's Shield Tower in Eastern Plaguelands. It is only available to players who completed The Active Agent prior to Cataclysm. To exchange Rune of the Dawn for Seal of the Dawn, destroy the Rune and then ask Betina for another trinket.