Taken 13/05/18; Seems a bit of an oddity to me. It doesn't look to be from a ex-L&SWR box, plus there are boxes at all four Watercress Line stations so surely another box isn't needed (although in my admittedly limited experience S&T departments will always push for more?. Maybe it will be fitted with a frame and used to demonstrate signally practice?
Uploaded to Flickr by Clive G' on 17 May 2018
Photo © Clive G', 17 May 2018. Licensed for reuse under this Creative Commons licence