A hazmat shipment includes a package with the UN identification number and proper shipping name stenciled directly on its surface, a 4-inch diamond-shaped hazard symbol on its side, and the trailer hauling it displays matching 9.84-inch (250mm) diamonds on all four sides. Which of these three is the 'marking'?

49 CFR Part 172, Subpart D (Marking) and Subpart E (Labeling); 172.519(c)(1) (placard size); AAMVA CDL Manual Sec. 9.3.7

Inspectors and first responders check all three separately, and mixing them up on a knowledge test is one of the most commonly missed questions. Markings tell you exactly what the material is, while labels and placards tell you the hazard class at a glance — a driver who can't tell them apart can load, label, or placard a vehicle wrong without realizing it.