Mark of Sargeras

Mark of Sargeras drops from high-60 level mobs in Blade's Edge Mountains, Netherstorm, Shadow Labyrinth, and Shadowmoon Valley.

Popular farming spots include:
 * Death's Door - Blade's Edge Mountains
 * Forge Camp: Anger - Blade's Edge Mountains
 * Arklon Ruins - Netherstorm ( drop rate may have been nerfed)
 * Legion Hold - Shadowmoon Valley
 * Forge Base: Gehenna - Netherstorm
 * Forge Base: Oblivion - Netherstorm
 * Shadow Labyrinth - Auchindoun
 * The Arcatraz - Tempest Keep
 * The Mechanar - Tempest Keep

As a quest objective
Marks of Sargeras are used for these quests to increase reputation with the Aldor (and decrease it with the Scryers):