Maintenance. The issuance of a permit shall not relieve the owner or lessee of the premises from the duty of maintaining any such structure. Every sign constructed or maintained shall be plainly marked with the name of the person, firm or corporation erecting or maintaining such sign. All signs shall be painted, properly illuminated and maintained in good repair at all times. Any sign that is or shall become dangerous or unsafe in any manner whatsoever shall be repaired and made safe, in conformity with this chapter, or shall be removed by the owner, lessor, agent or occupant of the building, property or land upon which it is placed or to which it is attached. A written notice shall be served upon the owner, lessor, agent, or occupant of a building, property or land upon which a dangerous or unsafe sign is located. Said notice shall require necessary action to be taken within 10 days from the date of the service of the notice upon such person or within such lesser time as shall be deemed reasonable in the case where the danger to public health, safety and general welfare is so imminent as to require more immediate abatement.