Holy Nativity - JOY Yard Sign Letters - Merry Christmas Yard Décor for Christmas Holiday Winter Decorations Outdoor with Metal Stakes. Economical and durable, our Coroplast Yard Signs are a staple of outdoor advertising. These outdoor JOY Outdoor Letters full color direct printed graphics are vertically fluted for use with a Stakes. Coroplast is typically used for yard, parking, real estate, and election signs. They are waterproof.