Signs, including billboards, conforming to the regulations prevailing prior to the effective date of this amendment, but which do not conform with the regulations herein or subsequent amendments thereto, shall be nonconforming signs. Any sign or part thereof which has blown down, been destroyed, needs to be changed due to a change in business or otherwise taken down for any purpose other than repair, shall not be rebuilt, reerected or relocated unless it complies with the provisions of this section and other applicable regulations.