I recall from somewhere - but can't remember exactly - that the dots indicate that the specific switch is a "3 Position Switch."
All others LIGHT SWITCHES are simply on / off.
Edited. We're talking about light switches normally used on the overhead panel which do something MORE than simply turning a light on (ie: Extension / Retraction). Also, not switches that include any type of guard or are otherwise protected from movement except in unusual circumstances.
Last edited by Jimmy Do Little; 5th Aug 2009 at 11:06.
Reason: Assumed the obvious, but need to clarify.