Valentines Day Yard Sign 24" x 18" - Coroplast Valentines Yard Decoration for Happy Valentine's Day Party Outdoor Yard Sign with Metal H-Stake. Economical and durable, our Coroplast Yard Signs are a staple of outdoor advertising. These outdoor 24" x 18" Happy Valentine's Day Lawn 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.