The Fiery Hand is a group of slave soldiers employed as guards for the red temple of R'hllor in the Free City of Volantis. The Fiery Hand contains a thousand soldiers, never more and never less. Each of these soldiers is a slave of R'hllor. They wear ornate armor over their orange robes, and wield spears with points shaped as writhing flames. As per custom of Volantis, these slaves have flames tattooed across their cheeks.
A Dance with Dragons
Five soldiers of the Fiery Hand escort the priest Moqorro aboard the Selaesori Qhoran. Only three of them survive the storm that wrecks the ship. They are brought to the slave auction held outside of Meereen. Tyrion Lannister believes that the flames tattooed upon their faces will ensure some red temple will purchase them from the slavers.