Thank You Doctors Yard Sign Decoration, Coroplast Thank You Doctor Appreciation Week Yard Sign Outdoor Lawn Decorations with Metal H-Stake. Economical and durable, our Coroplast Yard Signs are a staple of outdoor advertising. This Thank You Doctors Yard Sign Decoration 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.