In message .com,
Mizter T writes

1935
'Fixed stop' system for buses introduced
First LT programme of compulsory and request bus stops started"
~~~~~

I'm not an expert on bus stops but I do know they're a surprisingly
late innovation - the above suggests as late as 1935, in London at
least.

I think that reference is simply to the LPTB's policy to rationalise
(using the "roundel" logo as a brand) the bewildering variety of signs
inherited from their bus and tram predecessors.

Signs were not always used if the place to wait was fairly obvious, such
as outside a pub or railway station, but elsewhere there were
rectangular plates attached to lampposts, triangular signs, discs on
poles, elaborate wrought-iron contrivances and, in the early 30s,
"tombstone" shapes (rectangular lower half with curved top).
--
Paul Terry