Abstract: An electronic warning system made up of illuminated and colored placards for trailers carrying hazardous materials. The colored placards are changed as desired to signal different hazardous loads by a computerized control unit located in the cab. The placards are based on display panels of either light emitting diodes or liquid crystal. A remote mobile control unit can also be employed by itself or in conjunction with the cab's control unit to operate at least four colored placards on each side of a trailer to collectively identify the hazardous cargo being transported in compliance with federal regulations.