There's no rules requirement for the heads to be on one side of the mast or the
other. This is an observation based on a few specific limited locations but it
seems like it's common for the heads to be mounted on the side away from the
tracks. For signals on a bridge structure, often to the right side of the mast
(the masts being located to the right-hand side of the track they control).
As for staggered block signals, top head to the left, bottom to the right
seems common, but I've seen both ways, particularly on double track where the
signals are opposite on opposite sides of the track, and the signals in the
reverse direction on the rear of the mast are opposite those on the "front",
while viewing.
Chris vanderHeide
Sarnia, ON
