The department is directed to mark the appropriate exit to eligible facilities by erecting two (2) identifying signs of a size and color suitable for ready observation by the motorist on the interstate highway. The first of these signs shall be placed a proper distance before the exit and the second shall be placed at the exit and may be incorporated into the directional sign normally erected to indicate the city or connector route served by the exit. The signs shall be erected facing both directions of travel on the interstate route.