Griswold got his start in 1923 with the invention of the "American Bobby," a traffic sign designed for placement in the middle of an intersection that would collapse if struck by a vehicle.

Signs were nicknamed after London traffic control officers with its red and green lights visible in all directions.

An approaching train would trigger not just the requisite red flashing lights and bells, but a mechanism that rotated a yellow stop sign ninety degrees to face traffic as well.

The firm purchased Los Angeles–based Magnetic Signal Company in the late 1940s and moved production to Minneapolis.

Management, sales, and manufacture of crossing signals continued in Minneapolis until 2000, when the division moved to Kentucky.