Mich. Comp. Laws § 445.620

Sec. 10. To enforce a lien that attaches under section 9, the moldbuilder shall give notice in writing to the customer and the molder. The notice shall be given by hand delivery or certified mail, return receipt requested, to the last known address of the customer and to the last known address of the molder. The notice shall state that a lien is claimed, the amount that the moldbuilder claims it is owed for fabrication, repair, or modification of the die, mold, or form, and a demand for payment.