An elongated flexible tube of resilient plastics material includes an upper end portion and a lower end portion and is capable of being repetitively bent through an angle of ninety degrees and of returning to an upright straight position with the aid of a flexible erecting member within the tube. The upper end portion may be thermally flattened for receiving a panel of reflective material or the reflective material may wrap around the tube. In one embodiment, the lower end portion of the tube projects into a hole within the ground and carries outwardly projecting spring fingers which positively lock into the ground. In another embodiment, a molded plastic base member releasably retains the lower end portion of the tube and is adapted to be cemented to a roadway surface. Also disclosed is a tool for quickly forming a series of holes within the ground to receive the lower end portions of the tubes.