I was drawn to the term 'Low Speed' and I wondered in what context it was used until I saw the diagrams and they are shunting signals which according to the NSW G.A pt 2 are called 'Position Light Shunting Signals.'
They come in 2 styles, one was triangular and the other was vertical, one light on top of the other.
The Triangular case type was both Ground and Mast mounted, depending on its location.
One the triangular version the 2 lights on the bottom display RED while the upper would show Yellow or Amber in most situations.
On top of the case could be mounted 2 or more 'boxes' that displayed a letter indicating what line it was cleared for, like UM for Up Main etc.
I would not be surprised to see that the physical appearance of these signals was the same in both States.
As usual, NSW shunting signals had a complicated history.
The "triangle" (Position Light) shunt signals were first introduced about 1960 at Granville and Gosford, and replaced older electrically operated semaphore "banner" signals enclosed in glass cases. They displayed lights similar to BR signals, and to begin with did not have route indicators where there were more than one route, or the only route was for a wrong line more. The lights were:__
* Stop = red and white horizontal
* Shunt = two white at 45 degrees.
Because of problems with white lamps looking a bit yellow, various shunting and main line signals with white marker lights and the "band of lights" for junctions, were altered to replace the white lights, and the "triangle" shunt signal was altered as follows:--
* Stop = two red lights horizontal.
* Shunt = one yellow light in the top lampcase.
Over several decades, the "triangular" white shunt lamps were converted to the yellow pattern, AFAIK Gosford was the last to be converted.
Gradually route indicators were made universal, though Gosford still has some shunt signals with no route indicators.
When the Tulloch Double Deck trains were introduced in 1964, there was insufficient space between the tracks at 12 foot (3.66m) track centres, and a new design of signal had to be introduced. This was the "dwarf" signal with 3 lamps on top of one another. The top and bottom lamps were red, while the middle lamp was yellow. The is space on the top for no more than
two route indicators, and if more routes are needed, then "miniature multi lamp" route are needed.
If the "triangular" or "dwarf" shunt signals are facing moves on main lines, there will also be a green light when the track is clear to the next main line signal, and the next main line signal is clear. An early such signal at Sutherland in the facing direction has/had no such green light.
The "dwarf" signal case is also used for other purposes, even where track centres are not a problem.
* departure signals at some "automatic" crossing loops on the Broken Line.
** AFAIK, where a "dwarf" departure signal leads to a section not fitted with Rail Vehicle Detection, the yellow light is replaced with a flashing white light.
** See: Yarrabandai - http://www.sa-trackandsignal.net/Pdf%20files/ARTC/AR411.pdf
* co-acting signals, such as Chatswood Platform 3 southbound.
Shunt signals of either kind had one red light (the Marker light) fitted with a series resistor, so that with incandescent lights, it would burn a little less brightly, and take more time to burn-out. This doesn't apply to LED lights.
It is noted that BR has been converting its "triangular" signals to the R/Y/R pattern used by NSW.