Created in 1941 by Harold Forster, an artist noted for his illustrations on pre-war Black Magic chocolate boxes, KeepMum SheÂs Not so Dumb is typical of Second World War British propaganda attempts to instil caution in the public through humorous,memorable slogans, rather than through fear-inducing images of spies and saboteurs. Today, of course, this particular slogan appears ratherchauvinistic.