No person shall operate on a public road a minibus, bus or goods vehicle which, according to the registration certificate thereof was registered for the first time prior to 1 January 1989 and of which the gross vehicle mass does not exceed 3 500 kilograms, unless there is displayed in a conspicuous position on the left side thereof in letters and figures of not less than 40 millimetres in height and which shall be clearly legible at all times—

Provided that if such vehicle is fitted with a plate as referred to in regulation 245, the provisions of this regulation shall not be applicable to such motor vehicle.