[Semaphore signal]

Semaphore signal on display at the Saskatchewan Railway Museum. Semaphore signals "used a mechanically controlled blade and three coloured lenses that covered a lamp as the blade moved. Three indications were possible with a semaphore signal. Proceed when the blade was vertical and the lamp green, approach when the blade was at 45 degrees and the lamp yellow and stop when the blade was horizontal and the lamp red. Originally, white lamps were used for proceed and green for approach. This practice was discontinued because it was discovered that if a red lens broke the lamp would show white and a train might proceed when it should have stopped." http://www.saskrailmuseum.org/