Every officer, elected or appointed, to any City office, before entering upon the duties of his or her office, shall take the oath of office prescribed by the Constitution of the State and shall file the same with the City Clerk. In case of failure to comply with the provisions of this section within twenty (20) days from the date of his or her election or appointment, such officer shall be deemed to have declined the office and such office shall be declared vacant. It shall be the duty of the City Clerk to notify every officer elected or appointed to any City office of the requirements of this section. Such notice must be given within at least seven (7) days after such election or appointment, and must he served by a police officer, who shall take a receipt for the same, to be filed with the City Clerk.