Letters and Colors.
—The letters should be clear and distinct; the style known as block letter is good. The colors should be highly contrasting. Black and white is as good as any; however, Eno[230] thinks that black with yellow and red with white are the best combinations; yellow on black being better than black on yellow. Eno would classify signs as:
Primary, those for warning and directing moving vehicles, vivid yellow letters, arrows or graphics, on a black background.
Secondary, those for stationary vehicles, designating public parking spaces, cabstands, car and bus stops, etc., black on yellow background.
Tertiary, those for the control of pedestrians, designating crosswalks, safety zones, etc., red on white background.