Having passed through Harrow-on-the-Hill on a regular basis Ive noticed that second stopping board displaying "S:R" just nestled under Signal JB51/52 (Platform 5 Southbound local starting to Fast or Local lines). What does it denote and what movements does it enable? Could only find a video that shows the board which is seen at 21:52.
It was mentioned in a thread the other day that "S:R" boards indicate the stopping position for S stocks about to undertake a reversing move, i.e. if you stop there then the train is berthed correctly and the cab at the other end of the train is in right position to view the relevant signal.
The essential things in life are seen not with the eyes, but with the heart. --Antoine de St. Exupery