Alternate Blank Placards It’s important to identify hazardous materials while in transport by marking with warning placards. Placards are 10-3/4” x 10-3/4” and must be on all four sides of the vehicle. Every placard includes the color, symbol, and name of the class into which the hazard falls. The numbers are displayed inside the placard. Customize your alternate blank placards with pressure sensitive vinyl numbers.