Each wrecker service on the rotation list must place a sign on the door of each of its wreckers indicating the name, address and phone number of the service. This sign shall be painted on the door of the wrecker or otherwise permanently affixed to the door. The letters of the sign must be no less than two (2) inches high. If the wrecker is registered in a name other than that of the wrecker service, the owner's name must also appear on the door in letters no less than one (1) inch high. All lettering on wreckers shall be plainly visible and shall be in a color which contrasts to that of the wrecker.