Michigan Compiled Laws, Chapter 252. Highways § 252.307b

Sec. 7b. (1) Notwithstanding anything in this act to the contrary, the department may issue a permit for a directional sign for a publicly or privately owned activity or attraction that is nationally known or regionally known, that is of outstanding interest to the traveling public, and that is generally considered to be 1 of the following:

(2) A permit issued under this section is exempt from section 7a,  1 is not transferable, and is not eligible to be surrendered for an interim permit.

(3) A permit issued under this section shall be for a sign that is no larger than 150 square feet in size, no more than 20 feet high, and no more than 20 feet long, including border and trim and excluding supports.

(4) A sign for which a permit is issued under this section shall not be any of the following:

(5) The department shall not issue a permit under this section if there are more than 3 signs identifying the same activity or attraction facing the same direction on either side of the road along a single regulated route approaching the activity or attraction.

(6) The message displayed on a sign for which a permit is issued under this section shall only identify the activity or attraction and directional information useful to the traveler in locating the activity or attraction, including mileage, route numbers, and exit numbers. The message displayed on a sign for which a permit is issued under this section shall not include descriptive words or phrases or pictorial or photographic representations of the activity or attraction or the surrounding area.