Question A placard indicating hazardous materials is which shape? Answers Diamond Triangle Circle 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: Alaska HazMat Arizona HazMat Idaho HazMat Louisiana HazMat Maryland HazMat Minnesota Tank Missouri HazMat Oklahoma HazMat Tennessee Tank Vermont HazMat Wyoming Tank