Based on drawing by Greg Edwards of http://www.goldweb.com.au/~datashet/, this is a nameable NSWGR KM Post. Modern (post 1990s) practice is to only have these posts appear on the 'down' (left heading away from Sydney) side of the line only with just a plain vertical rail on the opposite side (also painted white). This is for reason of worker's safety, so they know which direction of the line is 'up' and can be prepared for timetabled trains to pass through the worksite.