"Private Property - No Unauthorized Access" Sign By SmartSign | 12" x 18" 3M Diamond Grade Reflective Aluminum 3M AUTHORIZED. Authorized signs are certified to the 3M Matched Component System. This assures that signs are durable outside. DURABLE ALUMINUM. Signs use 3M reflective Diamond Grade film mounted to 63 mil thick aluminum and last up to 12 years for indoor or outdoor applications. LAMINATED. Graphics are protected from weather and abuse. Graffiti can be cleaned off. Laminated signs outlast competitive unlaminated or overcoated signs. GIVE A HEADS UP. Convey your No Unauthorized Access warning with this Private Property sign - before you have to intercede personally. INSTALLATION. All signs have pre-punched/pre-cleared holes to ensure hassle-free installation. Signs mount to U-channel posts, square or round galvanized posts, wooden posts and chain link fences.