Abstract: A apparatus for providing a motorist advisory function similar to that of a flashing illuminated advisory sign, the apparatus having an electrically operable optical shutter positioned by means of a frame between one or more message signs and a viewing region. The optical shutter is made of a liquid crystal plastic material having a substantially opaque state, in which the message sign is not visible from a viewing region, and a transparent state in which the sign is visible over a relatively wide viewing angle. The state of the optical shutter is controlled by a flashing power supply circuit, the transparent state being achieved when power is applied to the optical shutter and the substantially opaque state being achieved when no power is applied. Several embodiments show use of the invention with conventional stationary message signs, a moveable message sign, and an embedded highway marker.