Because I have just noticed the signal line # in smart trains. It is in upper left corner in the lines rules menu. And the train will tell the smart station what line it is from.
So now I am trying to figure out how this can be used to handle several depots.
This is a short post because I have just now noticed it, and this is how far I have gotten so far.
![Smile :)](./images/smilies/icon_e_smile.gif)