"Danger - Roof Access, Authorized Personnel Only" Sign by SmartSign | 7" x 10" 3M Reflective Aluminum 3M AUTHORIZED. Our signs are fabricated under the audited 3M Matched Component System providing the best warranties and the most durable signs. DURABLE ALUMINUM. Signs use 3M reflective Engineer Grade film mounted to 40 mil thick aluminum. Signs have 7 year durability backed by a 3M warranty and rustproof aluminum. ROUNDED CORNERS. Signs have rounded corners and burr-free corners for safe handling, longer life and a professional appearance. INSTALLATION. Signs have pre-punched and pre-cleared mounting holes for easy installation. Signs mount to chain link fences, walls and doors.