This command enables railroad visibility mode, in which all railroads are highlighted for better viewability. This is a toggle command - run it again to turn it off.
The syntax for the showrails command is as follows:
showrails DLC: Hearts of Darkness
Find below working examples of the showrails command.
If showrails is disabled (default), running the above command will enable it, causing railroads to be highlighted on the map. If showrails is enabled, running the above command will disable the setting.