In message
, at
01:52:29 on Fri, 19 Jun 2009, Mizter T remarked:
And getting back to the original theme of "reporting in", the police
boxes were 2-way, with the flashing blue light indicating that an
officer should call the police station and see what was wanted.

I presume this is the origin of the flashing blue light on police
vehicles?

Blue is used in many ways as a "police colour". But originally,
emergency vehicles didn't have flashing lights, just a bell. The early
flashing lights used a rotating reflector, a bit like a tiny lighthouse,
to produce the effect.
--
Roland Perry