Stay Off Grass Yard Sign- Coroplast Visible Text Long-Lasting Please Keep Off Grass Yard Sign with Stakes. Economical and durable, our Coroplast Yard Signs are a staple of outdoor advertising. These outdoor Keep Dogs Off Yard Sign full color direct printed graphics are vertically fluted for use with Stakes. Coroplast is typically used for yard, parking, real estate, and election signs. They are waterproof.