Darkspeak

Darkspeak is an inaudible language originating from the underdark population of Svartalfheim, then spreading to the darker surface regions of the northern elven lands, while a nonverbal version is used by the Dwarves underground in Nidavellir. The glowing amber eyes of the Night Elves use short and long blinks to communicate in silent darkness. Vanir are known to use lamps or magical means in the same manner, while the Dwarves use tapping in the rocky tunnels to communicate over a distance, even when they cannot see who they are speaking to (rather handy in a cave-in).

The Morse Code of the Realm.