What is the difference between a 'label' and a 'placard' in hazmat regulations?

Labels are diamond-shaped markings (4 inches per side) applied to individual hazmat packages — boxes, drums, cylinders, IBCs. They communicate the hazard of that specific package to anyone handling it (warehouse workers, shippers, dock workers). Placards are larger diamond-shaped signs (at least 10.75 inches per side) applied to the outside of vehicles, freight containers, rail cars, and large bulk packagings. They communicate the hazard of the load to other road users, emergency responders, and inspectors. Both use the same color and symbol system for each hazard class — a flame for Class 3, a skull for Class 6.1, etc. — so the visual language is consistent from individual package to whole vehicle.