20 Iconic British World War II Propaganda Posters
3. "Careless Talk Costs Lives - You Never Know Who's Listening!" (1940)
One of a number of posters designed along this theme, the phrase "Careless talk costs lives" was intended to discourage people from gossiping and possibly revealing secret information for fear of spies listening in.
The designer Fougasse (i.e. Cyril Kenneth Bird) encouraged the government to use humour in posters in order to persuade people to co-operate without appearing to preach to them.