Lighting and color. Signs shall not resemble, imitate, or approximate the shape, size, form, or color of railroad or traffic signs, signals, or devices. Signs shall not obstruct or interfere with the effectiveness of railroad or traffic signs, signals, or devices. Signs shall not be placed so as to obstruct or interfere with traffic visibility, nor be lighted in such a way as to cause glare or otherwise impair driver visibility upon public streets. Signs may be illuminated.