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." Take a FREE Practice Test Now This questions appears in the following tests: Arkansas HazMat , Idaho HazMat , Iowa HazMat , Kentucky HazMat , Louisiana HazMat , Maryland HazMat , Missouri HazMat , New Mexico HazMat , Vermont HazMat , Virginia HazMat ,