GWR 2-6-0 'Aberdare' class 2-6-0 no. 2626 - LPC postcard

The 'Aberdare' class was built between 1900 & 1907 and most had been scrapped by 1938. 2626 was not one of those remaining at that time. The socket type of lamp holder was replaced by the vertical bracket soon after the Aberdares were built. The Great Bear, built in 1910, was outshopped with them in place. So this is an early photo. Talking of lamps, the ones stored on the running plate between the springs, include at least 2 with 'S' on them. It doesn't look as if that was the front face, through which the light would shine. Does anyone know the significance of the 'S'?
I terms of location, none is given, but there used to be tall rows of terraced houses like these ones on the approaches to Paddington.