Hornby TT:120 TT8046 Distant Signal
The yellow arms signify 'distant' or 'caution’ and are seen on the approach to a station or signal box, often being placed up to a mile from the signal box, depending on the speed of approaching trains.
As train speeds increased so drivers needed extra warning of the state of the line ahead than could be provided by the sighting of the actual stop or home signal. Distant signals were provided to give this advanced warning, at a distance. When set to the normal horizontal position the signal warned drivers that the signals ahead were not cleared for his train. The distant signal could only be 'cleared' to the diagonal position when all of the stop signals ahead were cleared for a train to pass into the section towards the next signal box or station.