How many identical placards is a vehicle hauling hazardous materials required to display and where?

Commercial Driver License

How many identical placards is a vehicle hauling hazardous materials required to display and where?

One (1), on the rear of the vehicle only.
Two (2), one on the front and one on the back.
Four (4), two on the front and two on the back.
Four (4), one on the front, one on the back, and one on each side of the vehicle.

Tags: Hazardous Materials Test