A vehicle placarded for hazardous materials must have placards on ____ sides.

Placards are used to warn others of HazMat. Placards are signs put on the outside of a vehicle and on bulk packages, which identify the hazard class of the cargo. A placarded vehicle must have at least 4 identical placards. They are put on the front, rear, and both sides of the vehicle. Placards must be readable from all 4 directions. They are at least 9.84 inches (250mm) square, square-on-point, in a diamond shape. Cargo tanks and other bulk packaging display the ID number of their contents on placards or orange panels or white square-on-point displays that are the same size as placards.
[COMMERCIAL DRIVER HANDBOOK]