One who announces. Specifically: An officer in the church of Constantinople, whose business it was to inform the people of the festivals to be celebrated. [1913 Webster]
An indicator (as in a hotel) which designates the room where attendance is wanted. [1913 Webster]
annunciator, n.
1 a device giving an audible or visible indication of which of several electrical circuits has been activated, of the position of a train, etc.
2 an announcer.