Ah ! we meet again :D many thanks.
A work colleague is in the process of taking some photos of Exeter psb, Exmouth Junc, Paignton and Crediton so hopefully I will be able to display them in the next few days.
A position light associated with a main stop signal is the two diagonal white lights that can be displayed on certain controlled signals.
They basically mean that when illuminated the signal can be passed at danger being prepared to stop short of any obstruction.
Its usual to find them...
I'm gradually compiling a variety of photos showing many of the uk's signalboxes.
If anyone else has photos they'd like to share with the rest of us please email them to me with a brief description at the link shown on my site and I'll glady include them.