All advertising signs, business signs, or bulletin boards not in accordance or in compliance with this Article which were in existence prior to the adoption date of this Title, shall be exempt from this Article except that upon the change of ownership of any building or property having a nonconforming sign which was in existence prior to adoption date of this Title, or upon remodeling or renovating of the exterior of any building to the extent of greater than 50%, the nonconforming sign shall be brought into conformity with this Article and any other city, state, or federal regulations.