In specified districts, specified non-conforming signs, specific non-conforming uses of land with minor improvements, specified non-conforming objectionable uses, certain specific types of uses involving open storage or salvage, non-conforming adult establishments, or certain non-conforming public parking lots may be continued for a reasonable period of useful life as set forth in this Chapter, provided that after the expiration of that period such non-conforming uses shall terminate in accordance with the provisions of this Chapter.