Just after Monty and Mildred leave her house in the car for the first time they pull up to an intersection that has a diamond shaped stop sign with white letters on a red background. However, the octagonal shaped sign was adopted in 1922 (almost a decade before the film is set) by the American Association of State Highway Officials and used thereafter for "STOP" signs, in part so that drivers could recognize that it was a stop sign from behind and prevent confusion with other traffic signs, and from 1924 through 1954 were composed of black letters on a yellow background. It was changed in 1954 to the present white on red background to reflect the "red equals stop" of street lights.