"Key Drop" Sign By SmartSign | 6" x 12" Aluminum DURABLE ALUMINUM. Signs are made using 63 mil thick aluminum and do not bend easily. They have been proven to outlast the toughest of storms. Signs last over 10 years outside. ROUNDED CORNERS. Signs have rounded corners and burr-free corners for safe handling, longer life and a professional appearance. LAMINATED. Signs are laminated for superior outdoor durability, chemical and abrasion resistance. EASY TO INSTALL. Signs have pre-punched and pre-cleared mounting holes for easy installation. Signs mount to U-channel posts, square or round galvanized posts, wooden posts and chain link fences.