The term appropriate city official, as used in this article shall mean any city official or city employee designated by the mayor or other chief executive officer of the City of Chickasaw as the person to exercise the authority and perform the duties delegated by this article to the appropriate city official. Whenever the appropriate city official shall find that any building, structure, part of building or structure, party wall, or foundation situated in any such city is unsafe to the extent that it is a public nuisance, such official shall give the person or persons, firm, association, or corporation last assessing the property for state taxes and all mortgagees of record notice by personally serving upon such person, firm, association, corporation, or mortgagee a copy of the notice to remedy the unsafe or dangerous condition of such building or structure, or to demolish the same, within a reasonable time set out in the notice, which time shall be not less than 60 days, or suffer such building or structure to be demolished by such city and the cost thereof assessed against the property. In the event that personal service is returned not found after not less than two attempts, notice may be given by registered or certified mail. The mailing of registered mail notice, properly addressed and postage prepaid, shall constitute notice as required herein. Notice of such order, or a copy thereof, prior to the delivery or mailing of the same as required by the immediately preceding sentence, shall also be posted at or within three feet of an entrance to the building or structure, provided that if there is no entrance notice may be posted at any location upon such building or structure.