Any sign existing on the effective date of adoption of this chapter which does not conform with any provision thereof, shall be deemed a nonconforming structure which may be maintained upon its present premises as set forth herein. (Ordinance 79-3, codified herein as Chapter XXII, was adopted June 20, 1979.) The right to maintain any nonconforming sign shall be eliminated: a) if the sign is substantially destroyed; b) if there is a change of use, occupancy or ownership of the structure of use to which the sign applies; c) if there is any change in the physical dimension of the sign; d) if the sign box is removed for any other reason not specifically approved.