Officers and enlisted men and women may be warned for duty by stating the substance of the order, by reading the order to the person warned, by delivering a copy of the order to that person, by leaving a copy of the order at the last known place of abode or business of that person with some person of the age of discretion, or by sending a copy of the order or its substance to that person by registered mail directed to the enlisted man or woman at his or her last known place of abode or business or to the post office nearest thereto.
In addition to or in lieu of the foregoing, notice may be given by posting a copy of the order at the entrance to the nearest post office to the military or naval headquarters issuing the order, at the entrances of the city hall or county courthouse of the city or county where the headquarters are located, and by causing a copy of the warning order to be published in a newspaper of general circulation in that county.