The term "appropriate municipal official" as used in this article shall mean any municipal building official or deputy and any other municipal official or municipal employee designated by the mayor or other chief executive officer of the municipality as the person to exercise the authority and perform the duties delegated by this article. Whenever the appropriate municipal official of the municipality finds that any building, structure, part of building or structure, party wall, or foundation situated in the municipality is unsafe to the extent that it is a public nuisance, the official shall give the person or persons, firm, association, or corporation last assessing the property for state taxes and all mortgagees of record, by certified or registered mail to the address on file in the tax collector's or 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 or suffer the building or structure to be demolished by the municipality and the cost thereof assessed against the property. The mailing of the certified or registered mail notice, properly addressed and postage prepaid, shall constitute notice as required herein. Notice of the order, or a copy thereof, shall, within three days of the date of mailing, also be posted at or within three feet of an entrance to the building or structure. If there is no entrance, the notice may be posted at any location on the building or structure.