Sentence:  From time to time the <WSD>boardsman</WSD> has to don some descriptive costume. Should he be retained on behalf of the Army and Navy Hair-Cutting Saloon, he may appear in an old regimental tunic and cocked hat, accompanied by a mate who stalks the world in the guise of a British Admiral. Again, should his boards illustrate “The Convict's Doom,” the latest melodramatic success at the Princess's Theatre, he will very likely walk abroad in knickerbockers and a jacket plentifully embellished with the broad arrow. 
Meaning of the word marked with <WSD> tags:  One who wears a sandwich board.