Techniques for displaying messages on top of a vehicle are disclosed. Although useful in many other areas, the techniques are particularly suitable for taxicab. According to one aspect of these techniques, a display unit is mounted on top of a vehicle. The display unit includes at least two display panels...http://www.google.es/patents/US7449998?utm_source=gb-gplus-sharePatente US7449998 - Electronic display panels for automobiles
