Text on the DiamondPlate Signs (Engraved Aluminum Signs) is sealed into the aluminum core and cannot be abraded. Plates resist salt spray and chemicals. Due to the matte finish, the message is not hidden by glare. The 20 mil thick metal is anodized, a chemical process that makes the metal diamond-hard. Tough, waterproof signs are supplied with 3M 468 adhesive meant for permanent application.  Printed Aluminum Signs, on the other hand, available in 40 and 63 mil thickness, are screen printed with inks from 3M that match the same standards for traffic signs. The process involves attaching a stencil to a screen, flooding that screen with ink, and then running over the surface with a squeegee. These signs are laminated for extended life. Signs have pre-drilled holes for quick installation. Both the signs are fade-proof and durable. However, engraved signs are thinner than printed aluminum signs.