The term "appropriate city official" as used in this subpart shall mean any city building official or deputy and any other city official or city employee designated by the mayor or other chief executive officer of the city as the person to exercise the authority and perform the duties delegated by this subpart to appropriate city official. Whenever the appropriate city official of the city shall find that any building, structure, part of building or structure, party wall or foundation situated in any city is unsafe to the extent that it is a public nuisance, the official shall report the findings to the city governing body. At that time the city governing body shall determine whether the building, structure, part of building or structure, party wall, or foundation constitutes a public nuisance. Should the city governing body find by resolution that the building, structure, part of building or structure, party wall, or foundation is a public nuisance, then the appropriate city official shall give the person or persons, firm, association, or corporation last assessing the property for state taxes, by certified or registered mail to the address on file in the revenue commissioner's office, notice to remedy the unsafe or dangerous condition of the building or structure, or to demolish the same, within a reasonable time set out in the notice, which time shall not be less than 30 days unless an extension is granted by the appropriate city official or suffer the building or structure to be demolished by the city and the cost thereof assessed against the property. The mailing of the certified or registered notice, properly addressed and postage prepaid, shall constitute notice as required herein. The city shall place a sign or placard within 15 feet of the entrance of the building or structure, indicating that the city had declared the building or structure to be a public nuisance; however, if there is no entrance in which to place the sign or placard, then the sign or placard may be posted at any location upon the building or structure.