English: A Great Western Railway disc and crossbar signal at Didcot Railway Centre, England. This early form of mechanical signal was rotated to show one of two aspects to on coming trains. The disc represents 'all right' and the the crossbar represents 'stop'. On this one the extended tails on the crossbar were a later modification to identify signals protecting the down line (the one travelling away from London).
{{Information |Description={{en|1=A Great Western Railway disc and crossbar signal at Didcot Railway Centre, England. This early form of mechanical signal was rotated to show one of two aspects to on coming trains. The disc represents 'all right' and the