CPL history lesson

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Just a slight tangent - semaphore signalling is still
used reasonably extensively on the UK rail network,
mostly on lower speed regional lines - electrified
third rail and diesel operated - in SE and SW Enland,
East Anglia, Scotland, and even in the Greater London
area.

I don't believe I've seen any semaphore signalling on
US rail networks.

'Semaphore signal
The kind of signal in use in the UK before colour
light signalling (there are still many in use on less
used lines). The signal consists of an arm projecting
from a post. Danger or caution is indicated by the arm
being horizontal. A clear signal is indicated by the
arm being at an angle of about 45 degrees. There are
basically two kinds of semaphore signal - home and
distant. The arm of a home signal has a square end and
is coloured red with a white vertical stripe; if the
arm is horizontal it indicates danger and a train
approaching it must stop. A distant signal has a
fishtail cutout in its end and is coloured yellow with
a black fish-tailed shape black line. A horizontal
distant signal arm ("caution"), indicates that an
approaching train should be prepared to stop at the
next signal. At the post end of semaphore arms there
are "spectacle glasses" through which a parafin light
shows to indicate the state of the signal at night.'