225 ILCS 440/4.08

Signs, displays and devices giving specific information in the interest of the traveling public may be erected and maintained by the Department within the right-of-way on the Interstate System and on other freeways with full control of access in areas designated by the United States Secretary of Transportation, pursuant to Title 23, U.S. Code, Section 131 (f). Signs giving specific information regarding tourist oriented businesses in the interest of the traveling public may also be erected and maintained by the Department within the right-of-way on rural non-interstate and non-freeway State highways. Such signs, displays and devices shall conform to national standards promulgated by the Secretary pursuant to such authority.