Idaho Code § 40-513C

That portion of interstate highway I-90 located in Idaho is the Idaho portion of the national purple heart trail. The Idaho transportation department shall design and construct signs indicating the highway number, the designation as the purple heart trail, and any other appropriate information. The department shall erect a sign at each end of the highway and markers at intermediate sites along the highway that the department determines are appropriate. The department is required to design, construct, and erect the signs and markers only to the extent that moneys are provided for this purpose through private donations, grants, awards or other moneys.