Were the stop signs at one time black and white?
If so, when did they change to red and white and what was the reason?.
Stop signs began appearing in various American cities in the 1910s. In the early days, stop signs were not standardized, and in many cities black letters on a white background were used. The first national group to create rules standardizing stop signs, the American Association of State Highway Officials, convened in 1922 and developed the octagonal shape as the standard. At this time, stop signs had the word "STOP" painted in black on a white background. From 1924 to 1954, stop signs were made with a black "STOP" legend on a yellow field. In 1954, the white-on-red stop sign replaced the black-on-yellow version. Red already signified "stop" on traffic lights, so the move was meant to standardize red as a stop signal. In 1966, that standard became a national law.