Richard,
For information on UK prototype signalling try here:
http://www.signalbox.org/
For Trainz AI control of shunting moves it's no so much the signalling as the use of Trackmarks and Driver commands such as "Drive to Trackmark" and "Couple at Trackmark" that you need to look at. You may also need to use invisible signals to help the AI.
I'm not aware of a guide which shows how to do this.
Chris