The Complete Guide to Interpreting Your Dreams

by Stearn Robinson - Tom Corbett
The meaning of this dream varies considerably according to the details of its action, but as a general guide, signals represent the realization of long-delayed wishes or ambitions.

Mystic Dream Book

by Internet Archive - Anonymous
Waiting in a station for a train that is Signalled, is a portent of long delayed wishes that will at last be realised.

Dreamers Dictionary

by Garuda
Vision: Hearing a signal is a warning about impending events or certain people.

See Bell, Whistle.