Signs shall be maintained so as to be structurally sound and in a safe condition. Signs shall be kept in a state of undeteriorated appearance by means of painting, sealing or coating, and repair or replacement of damaged parts, panels, or lights. Signs which, by reason of deterioration, become unsafe or unsightly, shall be repaired or removed by the property owner upon written notice of the City or may be removed by the City upon written notice of the City.