Graduation 2021 Yard Sign 18" x 24" - Coroplast Graduation Yard Decoration Graduation Sign Class of 2021 Yard Sign with Metal H-Stake. Economical and durable, our Coroplast Yard Signs are a staple of outdoor advertising. These outdoor 18" x 24" Graduation Yard Decorations full color direct printed graphics are vertically fluted for use with an H-Stake. Coroplast is typically used for yard, parking, real estate, and election signs. They are waterproof.