What is used to warn people about hazardous materials? Before you start the test, please answer the question below regarding your insurance status. Without insurance you will not be able to drive in Ohio Do you currently have car insurance? Yes I have insurance. Great, you're all set! Click here if you still want to compare rates. No, I need insurance and I want to compare options. Question What is used to warn people about hazardous materials? Answers Placards Flashing lights Color-coded pieces of tape License plate stickers Explanation Diamond-shaped warning signs, called "placards," are placed on the outside of a vehicle carrying hazardous materials to serve as a warning. This questions appears in the following tests: Maryland HazMat Nevada HazMat North Dakota HazMat North Dakota HazMat South Carolina HazMat