What shape is a placard indicating hazardous materials? Question What shape is a placard indicating hazardous materials? Answers Diamond Triangle Circle Octagon Explanation In general, vehicles carrying hazardous materials are required to display diamond-shaped warning signs on all four sides. These warning signs are called "placards." This questions appears in the following tests: Colorado HazMat Connecticut HazMat District Of Columbia HazMat Georgia HazMat Indiana HazMat New York HazMat West Virginia HazMat