Shade, n. (from Irish "shéadóg" meaning "blower") - term used to refer to the Gardaí
Síochána or other law enforcement agency.
Comes from an era where gardaí carried whistles, which they blew to alert other gardaí and nearby civilians of crimes. The term "shéadóg" was commonly used to refer to gardaí (or other police) in the early 20th century. This became shortened to the English word "shade" in the traveller "gammer" slang, later becoming part of everyday usage.