Mich. Comp. Laws § 570.555

Sec. 15. Before enforcing a lien granted to an end user under section 13, notice in writing shall be given to the customer, delivered personally or sent by registered mail to the last known address of the customer. The notice shall state that a lien is claimed for the amount due for metal fabrication work or for making or improving the special tool. The notice shall include a demand for payment.