The banner signal was invented by W R Sykes & Co around 1900 as electrical operation of signalling was beginning to become a practicality.
The arm of the signal rotated on an opaque disc in an enclosed glass case, allowing lightweight operation in a clean environment. many early examples had red-coloured 'arms' and were used in place
of conventional signals at locations of poor lighting or limited clearance. However, with the arm being around a third of the size of a normal signal, they weren't really suitable for use on higher-speed
sections of line.However,unlike many adventurous signal designs, the banner signal did not become extinct. Instead, it was adopted nationwide as a 'repeater' signals, to show the position of a signal ahead
which might be obscured by station buildings or a bridge. Red-coloured arms continued to be used, initially, but around 1924 a change was made to using yellow arms for repeaters. The now universally accepted
use of black arms was introduced in 1929.This principle of repeating signal indications survives to this day - even in areas of colour light signalling - although the majority have now been replaced by
fibre-optic light signals which give the same indications without any moving parts.