"C" shaped clamps on SR rail built semaphores? (historic)

[4COR]

I was flipping between putting this in Infrastructure or in the Railway History thread - Mods, please move as you see fit!

Here is part of an image of a rail built home signal from around 1950 (image from anistr.com) - here we have the Up Section signal at Upper Warlingham (near the Maple Rd overbridge), with a 2 aspect approach light for Riddlesdown Tunnel Intermediate Box mounted down the post).

On the right hand rail post as viewed, there are two things that look like some sort of clamp, here looking a little like a reverse C shape, level with the platform behind the post. My question is, what are they?



There looks to be a similar one on this picture of the up platform starter, same location, this time on the right of the image (image from Mike Morant's website) - but I've not seen them anywhere else... Thanks for any enlightenment!

 

[Gloster]

I have had a look through Southern Signals and what look like the same gadgets only appear a couple of times. I can only suggest that they are boxes holding relays, possibly ones to prove that the signal is physically off. (That is only a very wild guess.)

 

[Railsigns]

They're contact boxes containing an electrical contact to prove the position of the semaphore arm. On Southern semaphore signals, they're usually positioned at the same height as the arm spindle.

I presume the second contact box on the second signal is used to extinguish the approach light when the semaphore arm is 'on' (I've seen similar on a photo of a signal at Tulse Hill).

 

[4COR]

Great - thank you both!