Rune of the Dawn

The Rune of the Dawn is a trinket that serves as an and increases magical damage 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 Seal of the Dawn 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 the Cataclysm. To exchange Seal of the Dawn for Rune of the Dawn, destroy the Seal and then ask Betina for another trinket.