OO/EM/P4 Stencil Indicator with the letters 'RA', meaning Right Away.
A 'right away' indicator is used at places where the driver may be unable to see the 'ready to start' handsignal, so this is operated by station crew.
There is a section behind the stencil, large enough for a Surface Mount LED, I would recomend a pre-soldered version, similar to this
. Designed using original tehnical drawing direct from Unipart Dorman (who suppy these to Network Rail) and its includes detail sush as the sighting tube. If you do intend to add an LED, I recommend painting te stencil black to prevent light bleed.
Other stencil indicators can carry the letters 'CD' for Close Doors or the word 'OFF' do show a signal is showing proceed. If you want me to do these, let me know and I will do it for no extra cost.