What you need is an occupancy detector for each electrical block of your analog DC layout. Once the detector finds a current flow it can operate signals, crossing gates, panel indicators or whatever through the proper electrical outputs.
The 'granddaddy' article(s) were Linn Westcott's description of his Twin-T detector. It was built with discrete transistors. Since then, there have been other articles. There are also several commercial detectors manufactured. Somebody who has tracked this more closely than I have can probably be more specific.
Chuck (modeling Central Japan in September, 1964)