Signalling Alteration Notices were provided for some signalling schemes, especially those that affected a large area or involved major changes in the signalling of a route. They usually took the form of a document detailing the changes, attached to a plan of the area involved – some of these were very extensive! Signalling notices are invaluable in the research of route signalling as they give a baseline at a known date, and often include information about fringe area signalling. Notices were numbered using a variety of schemes, and these numbers are listed in the following pages alongside the date and title of the signalling plan.