Nonconformities shall not be enlarged upon, expanded or extended, nor be used as grounds for adding other structures or uses prohibited elsewhere in the same district. A nonconforming use of a structure, a nonconforming use of land, or a nonconforming use of a structure and land shall not be extended or enlarged after passage of this Zoning Ordinance by attachment on a building or premises of additional signs intended to be seen from off the premises, except as provided in Section 1117.09(c), or by the addition of other uses of a nature which would be prohibited generally in the district involved.