No person shall carry out exterior alterations, restorations, reconstruction, demolition, new construction, or moving of a landmark or property within an historic district, nor shall any person make any material change in the appearance of such property, in its light fixtures, signs, sidewalks, fences, steps, paving or other exterior elements which affect the appearance and cohesiveness of the landmark or historic district, without first obtaining a certificate of appropriateness from the Historic Preservation Commission.