"A dark mysterious emblem found in Dol Guldur. This can be exchanged in Emyn Lum."
Quoted from: Aruen
This is a barter item which trades in for leggings that always have +30 Radiance on it. To equip the leggings, you must be level 65.
This item drops from the "Barad Guldur" raid instance (need boss name). In my opinion, you need to be level 65 and have 115+ Radiance to venture into Barad Guldur.