This mounting accessory allows an SIW-100 Room Availability Status Indicator or SSW Series Room Availability Hallway Sign to be attached to the mullion of an interior glass wall, window, or partition. It attaches to the left or right inside surface of a typical vertical, hollow metallic mullion. Alternately, it may be adhered directly to the glass or another flat surface (granite, marble, plaster, smooth stone or masonry, etc.) using the included two-sided adhesive pad.