The **direction indicators** are lights used to signal that a vehicle is going to turn or change lanes. These lights are yellow and flash intermittently. They are mandatory for all motor vehicles, as well as for trailers and semi-trailers.

For these lights to fulfill their function effectively, there must be at least **two lights** or an **even number** of them on the vehicle. This ensures that the vehicle can clearly indicate its intention to turn both right and left.

Additionally, in emergency situations, all the vehicle's direction lights are activated simultaneously to warn other drivers of a possible danger. This reinforces the need to have an even number of lights so that the signal is visible from all angles.

Therefore, the correct answer is that a car must have a **minimum of two lights** or an **even number** of direction indicator lights.