A "signal system" refers to a method or process of sending messages or information from one place to another. It is a way of communicating or transmitting data, usually through electronic means. Full definition
The $ 8 billion second phase consists of long - term improvements, including better subway cars, a new signal system and more modern communications technology. (observer.com)
A few attempts had been made to develop line - of - sight signal systems. (religion-online.org)
The MTA's frequently failing signal system relies on nearly century - old technology, and its train cars break down more often. (amny.com)