Annunciators

Here is what I got from D&RGW Communications engineer L.E. Trump:
Annunciators were usually homebrew devices of varying descriptions, that allowed the dispatcher to determine when a train passed a certain point without human intervention. These devices were ingeniously devised by the local linemen or signal maintainers, with help from the telephone and/or telegraph engineers, and usually consisted of some sort of track switch or track occupancy sensing device, and some sort of transmitter, either a code wheel on a Morse wire, or an open telephone transmitter located on a pole adjacent to the track that could "hear" the passing train, and put the signal on the dispatchers wire. Thus the DS could determine the exact time that a train passed a certain known point. The transmitting device had a unique sound or signal so that which was which was easily determined. Example: the annunciator at Whitewater station might come on the DS phone with a "didadidadidadida" tone for a short while as the train passed. Or, the annunciator at Summit station might come on the DS wire and send a string of Morse "S" characters, etc. Sometimes, the open telephone transmitter type would be located so as to "hear" a crossing signal from the train engine's whistle etc. These were handy devices, and never fell asleep, like a live "OS" operator out in the sticks might.