The service of any such order shall be made upon the occupant of the premises to whom it is directed by either delivering a true copy of same to the occupant personally or by delivering it to and leaving it with any person in charge of the premises, or in case no such person is found upon the premises by affixing a copy thereof in a conspicuous place on the door to the entrance of the premises. Whenever it may be necessary to serve such an order upon the owner of premises, the order may be served either by delivering to and leaving with the person a true copy of the order, or, if such owner is absent from the jurisdiction of the officer making the order, by mailing the copy to the owner’s last known post office address.