Abstract: A system for signalling conditions of, including an emergency within, a vehicle comprises a main housing mountable on the vehicle at a location visible from substantially all lateral points. A warning light is mounted within the housing and light which it generates is projected from the housing by an optical system as a plurality of substantially collimated beams each of which is oblique with respect to the major axis of the vehicle. A switch for actuating the warning light is located within the vehicle for unobtrusive operation. The system also includes additional signal lights for signalling different conditions of the vehicle and circuitry which prevents simultaneous operation of certain of the signal lights that have contradictory meanings.