It's always satisfying to come across a bit of left-behind hardware on a railway path, in this case a CR signal post base. OS maps confirm that there was indeed an 'SP' here, a little to the north of Murrayfield station. It would have been an advanced starter, if I understand these things.
Location: Murrayfield (former)
Original line: Granton Branch (Caledonian Railway)
Photographer: David Panton
Contact photographer: David Panton
Date: 09/01/2019
Image number: 67320