Luke has hit it on the head as to why we still have a visual ID on the car, say your car was stolen in a car jacking you flag a cop car down and say my green ford astra was stolen well there is a few thousand green astras in the city and it would take a thousand cops to find it.
This is true. Which is why all cars should have better theif deterrent systems, such as if you start driving the car while the alarm is going off or within 60seconds of it going off the steering wheel detonates a shotgun shell right into your chest. Brilliant.