Markings provide important information about the contents of a packaging, freight container, or transport vehicle and help warn of hazards posed by that material during transport. The markings give additional information, not provided by labels or placards, about the hazardous material in a package or vehicle.

Labels are printed on or affixed to packages containing hazardous materials. Color- and symbol-coded, labels provide easy and immediate warning of the hazardous materials inside a package. The Hazardous Materials Regulations (HMR) have specific requirements for design, use, placement, prohibitions, and exceptions for labels.

Hazardous materials placards correspond closely with the shape, color, and design of hazardous materials labels. However, placards are much larger than labels. Placards alert people to potential dangers associated with particular hazardous materials contained in motor vehicles, rail cars, freight containers, cargo tanks, and portable tanks.