Mich. Comp. Laws § 247.957a

Sec. 7a. No later than 1 year after the date the amendatory act that added this section is enacted into law, the department shall designate as Pure Michigan byways all routes that are designated as Michigan heritage routes on the date the amendatory act that added this section is enacted into law, if the department obtains a trademark license from the Michigan economic development corporation for the use of the words "Pure Michigan".