The signs were first used over 130 years ago, before people had radios. Railroads needed men to be able to send signals from far or near. Many times, the signal man would be too far away to use a whistle or horn. Colors, lights and hand signals were all used. On the railroad, different colors have meaning.
Flags are colored to send a message.
Blue - blue flags are placed on a car or other object on which men are working. Our pictures show a lantern, but men could also use flags or their arms. Lanterns allowed train crews to see signals at night. Swing lantern across tracks. Hold at arms length when train is moving.