Save the USPS Yard Sign - Coroplast Visible Text 2020 Election, Vote, Support The Postal Service USPS Yard Sign with Metal H-Stake. Economical and durable, our Coroplast Yard Signs are a staple of outdoor advertising. These outdoor Save the USPS Yard Sign 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.