Mich. Comp. Laws § 8.3q

Sec. 3q. The words "written" and "in writing" shall be construed to include printing, engraving, and lithographing; except that if the written signature of a person is required by law, the signature shall be the proper handwriting of the person or, if the person is unable to write, the person's proper mark, which may be, unless otherwise expressly prohibited by law, a clear and classifiable fingerprint of the person made with ink or another substance.