Hello Vonsworld and welcome to the forum.
The "switches" that you refer to are actually track datum plates.
Another member of the forum asked a similar question to yours some time ago.
http://www.railwayforum.net/showthread.php?t=3237
This is what the Network Rail Code of Practice says track datum plates should show:
• design level of the nearest rail of the track concerned;
• design value of the cant on the track concerned;
• horizontal design dimension to the running edge of the nearest rail of the track concerned;
• the track to which the marker refers if it is not the nearest track.