Apt Number Sign Stairway Numbers Sign apartment number signs are required by many state and city laws to identify the apartment number. the signs help distinguish the flats, apartment and suites of your building and make it easier for people to find its different accommodations. size 2.25 inch x 3 inch sign comes with a double side adhesive sticker-red sticker with strong adhesive force, sign thickness 0.4 mm, sign letters color: black. sign background color: brushed aluminum. sign material: aluminum sign type: door mounted