Hi , this is the reference of the kilometric point on the road.
See https://www.radars-auto.com/emplacements/seine-et-marne/la-houssaye-en-brie/4503-radar-autonome-d1036/#:~:text=Le%20radar%20autonome%20est%20install%C3%A9,par%20un%20panneau%20radar%20sp%C3%A9cifique.
This is the only way to reference a radar. Its position on the road