The period of time during which the following nonconforming uses of buildings, structures or land may continue or remain is limited to two years from the effective date of this Zoning Code, or of an amendment thereto which causes the use to be nonconforming. Every such nonconforming use shall be completely discontinued and all appurtenant or altered structures shall be removed from the premises at the expiration of the two-year period.
   (a)   A nonconforming building or structure having an assessed valuation not in excess of one thousand dollars ($1,000);
   (b)   All nonconforming billboards or outdoor advertising structures not attached to a building lawfully existing upon the effective date of this Zoning Code; and
   (c)   A nonconforming use of land where no enclosed building is involved, or where the only buildings employed are accessory or incidental to such use, or where such use is maintained in connection with a conforming building. This subsection does not include public or private parking lots established prior to the effective date of this Zoning Code.