No nonconforming structure or use shall be maintained, renewed, changed or extended until a Zoning Certificate has been issued by the Zoning Administrator. The Zoning Certificate shall state specifically wherein the nonconforming use differs from the provisions of this Zoning Ordinance. After enactment or amendment of this Zoning Ordinance, or after annexation of any area to the City, the Zoning Administrator shall notify in writing the owners of nonconforming uses about this requirement for a zoning certificate. Such owners shall have three months after receipt of notice to apply for a zoning certificate. Failure to make such application within three months shall be presumptive evidence that the property was in conforming use at the time of enactment or amendment of this Zoning Ordinance.