The custom is as fleeting as it is elusive. In a matter of a split second, the entire exchange is over, and the people who witnessed the covert operation often never even knew it happened. A challenge ...

Among bartenders and the cocktail-savvy, Fernet Branca is a bitter amaro with a reputation as a welcome shot, referred to affectionately as a “bartender’s handshake.” Fernet Branca didn’t coin that ...

Defense Secretary Robert Gates hands a challenge coin bearing his name to a service member at a forward operating base in Kandahar province, Afghanistan, in 2011. Photo by Jason Reed/Getty Images ...