"Speed Limit 15 MPH" Sign by SmartSign | 18" x 24" 3M High Intensity Grade Reflective Aluminum 3M AUTHORIZED. Authorized signs are certified to the 3M Matched Component System. This assures that signs are durable outside. OFFICIAL SIGNS. Buy the same signs sold to our governmental customers. Over 1,000 municipalities buy their signs from us. 18" x 24" signs meet the DOT MUTCD R2-1 Specs for Speed Limit Signs. 12" x 18" speed limit signs are not covered by the MUTCD standard. DURABLE ALUMINUM. Signs use 3M reflective High Intensity film mounted to 80 mils thick aluminum. All signs come with burr-free corners and 3/8" punched and pre-cleared holes. Signs do not have a low-cost plastic core. LAMINATED. To achieve maximum durability, sign graphic are protected with a 3M traffic sign laminate. This provides enhanced weather and graffiti resistance. INSTALLATION. Signs mount to U-channel posts, square or round galvanized posts, wooden posts and chain link fences.