After meeting Wrathion and sharing a drink with him, he gives you a quest that requires you to collect Sigil of Power x 10 and Sigil of Wisdom x 10.
When LFR opened for testing tonight, we found that Sigil of Power drops from every boss 100% of the time. It appears as a quest objective in the tooltips for most bosses in Raid Finder difficulty, but drops from all of the bosses that have been killed so far.
Earlier today, we saw that Sigil of Wisdom appeared as a quest objective on Grand Empress Shek'zeer's tooltip in 25 Man Normal Difficulty Heart of Fear. Unfortunately, no one was able to kill her to confirm that it actually drops. Keep in mind that this is beta and things can change in the future and may not be working as intended.
Once 10 of each Sigil has been collected, Warthion sends you into the Terrace of Endless Spring to defeat the Sha of Fear. Before entering the Terrace of Endless Spring, you must have completed the Heart of Fear raid. Upon defeating the Sha of Fear you will loot a Chimera of Fear from him and bring it back to Wrathion.
When the items that you collected are combined, you will be able to choose from a Crystallized Dread, Crystallized Horror, or Crystallized Terror gem. These gems are unique equipped, and go into a Sha-Touched socket in the weapons below. These weapons drop from bosses in Terrace of the Endless Spring and the last boss of Heart of Fear.