Final answer:
Motor vehicles must have turn indicator lamps to signal their intended direction and maintain road safety. This requirement is mandated by traffic laws to prevent accidents and ensure communication with other road users.
Step-by-step explanation:
Motor vehicles are required to have turn indicator lamps or devices to ensure the safety of both the driver and others on the road. These signals provide a warning to other road users of a vehicle's intended direction of travel, thereby helping to prevent accidents. According to traffic laws in many jurisdictions, any motor vehicle used on public roadways must be equipped with turn indicators if the vehicle design warrants their use, specifically if the vehicle's operation involves public interactions where signaling is essential for safety reasons.