Whenever a non-conforming use of a building or structure, or part thereof, has been discontinued for a continuous period of six (6) months if the building was originally designed and constructed for a non-residential use, or whenever there is evident a clear intent on the part of the owner to abandon a non-conforming use, such use shall not, after being discontinued or abandoned, be re-established, and the use of the premises thereafter shall be in conformity with the regulations of the district.