Abstract: A traffic sign selectively displays and obscures information arranged permanently on the outer surface of a rear plate of a pair of rigid, transparent plates defining a closed cavity therebetween by displacing out of and into the cavity an opaque liquid contained in a closed reservoir which has an air-filled space over the liquid. A closed fluid conduit system connects the cavity with the reservoir and includes a first valved conduit connecting the air-filled space to the cavity, a second valved conduit connecting the liquid to the reservoir, a pressure release valve in the first conduit, and a control for selectively delivering liquid from the reservoir into the cavity through the second conduit while concomitantly withdrawing air from the cavity through the first conduit, and vice versa, whereby the cavity is rapidly and completely filled with the liquid to obscure the information and emptied of the liquid to display the information. The information is illuminated from the rear.