"Slow Down - Only You Can Prevent Speed Bumps" Sign By SmartSign | 12" x 18" 3M Fluorescent 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 fluorescent film mounted to 63 mil thick non-rusting 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. 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.