Reading the latest South Western Circle Monograph on the L&SWR use of low pressure pneumatic signalling by Stuart Isbister I came across the following-
“Upper quadrant signals were first introduced onto former L&SWR routes at Liphook on Sunday 25th March 1928”
Apparently no further conversion dates are recorded on “Signalling Notices” to train crew.
It also appears that about the same time distant signals generally were changed from red arms, to the now familiar yellow arm with black chevrons. The spectacle colours were changed to yellow and green (from red and green).
The description of a yellow distant signal, with arm in the horizontal position was referred to as being “at caution” rather than “at danger” as previously.