Truck Drivers Must Turn Off Engine, Set Brakes, Set Wheel Chocks Sign Mandatory Signs Specify that an instruction must be carried out. Symbols (or "pictograms") are depicted in white on a blue circular background. Sign wording, if necessary, is in black lettering on a white background. Mandatory signs comply to AS 1319 regulations. Truck Drivers Must Turn Off Engine, Set Brakes, Set Wheel Chocks Sign Mandatory Signs Specify that an instruction must be carried out. Symbols (or "pictograms") are depicted in white on a blue circular background. Sign wording, if necessary, is in black lettering on a white background. Mandatory signs comply to AS 1319 regulations.