Unknown 50v red pygmy indicator lamps

I found these recently on Ebay, they were quite oddly packaged coming in little ziplock bags with the contract stickers (included in the image) attached. These seem like ex-military stock, or possibly given that they are 50v they might be ex-GPO/telephone exchange lamps. These definitely seem like a custom order, as while the lamp bases seem to be very high quality the filaments seem quite crudely constructed!