A signaling apparatus including a substantially transparent panel, a light emitting element attached to a surface of the transparent panel, substantially transparent means for delivering power to the light emitting elements, and means for selectively controlling energization of the light emitting elements. The signaling apparatus being substantially transparent when the light emitting elements are not in an energized state. The light emitting elements might be LEDS, organic LEDS (OLEDs), electroluminescent displays, LCDs, or incandescent bulbs. The signaling apparatus is adapted to be mounted on a vehicle window for providing selectable patterns, variable rate flashing, changeable colors, textual or graphic messages, strobe lights, and other types of displays. Cooling channels or a cooling plenum may be provided to allow higher power (e.g., high intensity) operation.