Each taxicab shall be inspected at least once every six (6) months by a competent mechanic and his certificate of inspection shall be displayed in plain sight within the vehicle, showing that brakes, tires, steering apparatus, horn and lights have been inspected and found to be in good condition. Such certificate of inspection shall be signed by the mechanic making the inspection and by the chief of police every six (6) months. The chief of police may require an additional inspection by a competent mechanic of any such motor vehicle at any time he deems it necessary. (2000 Code § 16-205)