If you get into a taxi in Bangkok and see a mirrored ball hanging from the rear view mirror, you shouldn't get the wrong idea. It's not there to turn to the rhythm of Donna Summer or the Bee Gees on the radio, or to use to check if you have any pad Thai noodles stuck between your teeth. Mirrored balls in Asia, the kind found in homes, businesses, and cars (not the ones in the dance clubs) are commonly used in Feng shui. If you're not familiar with Feng shui, it means "wind-water", and is the ancient Chinese practice utilizing the laws of heaven and earth to help improve your life.
The mirrored balls are believed to reflect negative energy away from you, bringing you into alignment with harmony. In cars, the mirror reflects away evil forces that cause accidents. Another reason they're used in the taxis is because of the low ceiling which is believed to have a pushing down effect on you. The idea is that the mirror reflects the ceiling back before its pushing effect reaches you. The mirrors are also used to reflect natural elements outside, such as fresh air, back into the car.
When I see the mirrored balls in taxis, they give me a sense of well being. In some ways, they're not so different than the disco balls in the clubs. The disco music and dance club atmosphere also helps to release all that negative energy, and brings you back into alignment.