Abstract: A sign illuminator is described wherein a bundle of light conducting fibers are plied to a light diffusing plate having a plurality of recesses which receive the ends of the fibers in the bundle after the bundle is passed through an opening in the plate from an exterior side to an interior side. The plate is sized and shaped to conform to a channel in the sign so that when the light fibers are inserted into the light diffusing plate their light provides a back illumination for the sign. A light reflecting surface can be placed alongside the interior surface of the light diffusing plate to provide additional light use for the illumination of the sign. The sign can be letters or numbers or have such other shape as appears desirable.