"Keep Gate Closed, Dogs In Yard" Sign By SmartSign | 12" x 18" 3M Engineer 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 Engineer Grade film mounted to 63 mils thick aluminum and last up to 7 years outside. Signs do not have a low-cost plastic core. ROUNDED CORNERS. Signs have rounded corners and burr-free corners for safe handling, longer life and a professional appearance. LAMINATED. Graphics are protected from weather and abuse. Graffiti can be cleaned off. Laminated signs outlast competitive unlaminated or overcoated signs. INSTALLATION. All signs come with burr-free corners and 3/8" punched and pre-cleared holes. Signs mount to U-channel posts, square or round galvanized posts, wooden posts and chain link fences.