Ever noticed those numbers and diamond-shaped signs on trucks or containers? They’re UN numbers and hazmat placards, identifying hazardous materials inside—like flammables, explosives, or toxins. Each four-digit UN number pinpoints the type of material, while the color-coded placards (red for flammables, yellow for oxidizers, etc.) warn about its risks. These symbols help keep everyone safe, especially emergency responders. Think you know your hazmat signs? Take our GHS pictogram quiz and find out!