The term appropriate city official as used in this part shall mean any 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 part to the 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, accumulation and storage of junk, inoperable motor vehicles or parts of inoperable motor vehicles, abandoned dwellings and mobile homes, and litter around property and vacant lots, including, but not limited to, abandoned cars and appliances, situated in the city 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 notice by personally serving upon the person, firm, association, or corporation a copy of the notice to remedy the unsafe or dangerous condition of the building or structure, or to demolish the same, accumulation and storage of junk, inoperable motor vehicles or parts of inoperable motor vehicles, abandoned dwellings and mobile homes, and litter around property and vacant lots, including, but not limited to, abandoned cars and appliances, or to remove the same, within a reasonable time set out in the notice, which time shall be not less than 30 days, or have the public nuisance demolished or removed by the city and the cost thereof assessed against the property. In the event that the personal service is returned not found after two attempts, the notice may be given by registered or certified mail. The mailing of the registered mail notice, properly addressed and postage prepaid, shall constitute notice as required by this part. Notice of the order, or a copy thereof, prior to the delivery or mailing of the notice 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 the notice may be posted at any location upon the building or structure or the most appropriate site of the accumulation and storage of junk, inoperable motor vehicles or parts of inoperable motor vehicles, abandoned dwelling and mobile homes, and litter around property and vacant lots, including, but not limited to, abandoned cars and appliances.