sign having self - storing characters which are quickly changeable . the face of the sign has a patterned array of openings juxtaposed against a contrasting background . the background may be supplied by color contrast and / or by illumination . shutters are mounted for sliding or pivotal movement for selectively closing the openings so that the remaining exposed background areas define visual information such as symbols or characters . alternatively , the shutters may be rotatably mounted in the openings and have opposite sides which , respectively , contrast with and match the sign face color .