(1)  The driver of a vehicle must give a stop signal by means of the vehicle’s brake lights.

(2)  However, if the vehicle’s brake lights are not in working order or are not clearly visible, or the vehicle is not fitted with brake lights, the driver must give the stop signal by giving a hand signal in accordance with rule 55, or using a mechanical signalling device fitted to the vehicle.

Note Mechanical signalling device is defined in the dictionary.