door knocker
n.— «Officer Kushner did not find anyone at home.…Officer Kushner left a “door knocker” at the home requesting that defendant contact him regarding a complaint about the care and feeding of her animals. He also left several telephone messages for her.» —by North Carolina Court of Appeals Calloway v Onderdonk, No. COA02-1076 (Buncombe County) July 1, 2003. (source: Double-Tongued Dictionary)