No person shall carry out any exterior alteration, restoration, reconstruction, demolition, new construction or moving of a building designated as a landmark or any property within a historic district, nor shall any person make any material change in the appearance of such a property, its light fixtures, signs, sidewalks, fences, steps, paving, major landscape feature or design or other exterior elements which affect the appearance and cohesiveness of a historic district, without first obtaining a certificate or appropriateness from the Commission.