A lightweight, portable, reliable and functionally self-contained device for illuminating a sign is disclosed. The portable illuminated sign has particular application by realtors when selling real estate property, which has been listed. A method of onsite advertising and promotion of property available for sale comprising the steps of : providing an illuminated sign having a opaque or translucent face, a solar cell to generate power, a battery to store power, a lamp bulb, and a photo cell to turn power on to the lamp bulb in low ambient light; positioning the sign in a prominent location so that it can be viewed by passers by; and, removing the sign subsequent to sale of the property. In a preferred embodiment of the invention the sign comprises a duration control to specify duration of illumination after the photocell has turned on power to the lamp bulb. Multiple lamp bulbs as well as sign components are enclosed within a housing having translucent opposite side portions. This device has the adaptability to be installed onto existing signs.