a reflector includes a rotor disk rotatably mounted on a bike spoke having two semi - circular blades respectively formed on two surfaces of the rotor disk for driving a rotation of the rotor disk when subjected to a wind force when driving a bike , and having a retroreflective surface and a light - absorptive surface respectively formed on two opposite surfaces of the rotor disk for producing a flashing operation when rotating the disk , thereby providing a dynamic flashing reflector on a bike or the like for traffic warning or interesting purpose .