Image courtesy of David Backlin
From the 1956 annual report of the Missouri Highway Commission, this picture shows both the modern font and the older, square-ish fonts used on Missouri signs. This picture was taken at what is now Lindbergh Boulevard at Watson Road northbound near Kirkwood. Lindbergh was then designated Bypass US 67 and US 61, while US 67 went into the city of St. Louis along Loughborough and Kingshighway (for most of its length). Watson Road was designated US 50 and US 66 into the city of St. Louis. It's now Missouri 366.