Short for the words “hazardous materials”, hazmat related signs usually pertain to truck restrictions through tunnels or a heavily populated area where a hazmat related accident or spill would be detrimental to the immediate surroundings. Shields are in place now for hazmat preferred routes and banned routes. The signage is a white square with the letters HC in a green circle. When this logo is surrounded with a red circle and slash through it, that means that hazmat related traffic is prohibited from using that particular route.