An object or other sign left behind as evidence of having been present. The term alludes to the card left by visitors when the resident is absent or unable to receive anyone, a nineteenth-century practice. It was then transferred to an object or mark left at the scene of a crime that serves as the perpetrator’s “signature.” The notorious British criminal Jack the Ripper left calling cards on September 30, 1888, when he murdered two women, one a scrap of cloth and the other graffiti. This version has been widely used in mystery novels and television plays. A more current usage might be, “The insurgents leave roadside bombs as their calling cards.”