This is a Strieter-Lite reflector. A set of these reflectors mounted on posts near the side of a highway dramatically reduce the number of deer-vehicle collisions that may occur at dawn, dusk or night.

W
hen a car passes, light from the headlights is directed toward the side of the road and is seen by deer that wish to cross the highway as a row of sequential lights coming from the reflectors.

This startles them and causes them to run away or wait until the vehicle passes before crossing the road.