ETYM Latin annuntiator.
Indicates which electrical circuit has been active.
One that annunciates; specifically; a usually electrically controlled signal board or indicator.

ETYM Old Eng. herald, heraud, Old Fren. heralt, heraut, herault, French héraut, Late Lat. heraldus, haraldus, from (assumed) Old High Germ. heriwalto, hariwaldo, a (civil) officer who serves the army.
(Formal) A person who announces important news.