Michigan Compiled Laws, Chapter 252. Highways § 252.312

Sec. 12.(1) All persons holding permits under this act, at their own expense, shall place the permit number on each sign facing erected or maintained by them within 4 months after receiving a permit for signs existing on March 31, 1972 and within 3 business days for all other signs. The numbers shall be of a size and type specified by the department and located on the lower corner thereof nearest the adjacent highway.

(2) Any person who does not display the correct permit number or who does not display any permit number on a sign as required under subsection (1) is subject to a $250.00 penalty. The department shall give a person who is not in compliance with this subsection written notice of noncompliance, and a person not in compliance with this subsection shall have 30 days to remedy the violation before any penalty is assessed. A person subject to this section may verify compliance with the department via time-dated electronic means.