Dozens of World War II posters warn people at home and abroad about enemy eavesdropping. From cautionary admonitions ("Even in this friendly tavern there may be enemy ears") to humorous observations ("Even a fish wouldn’t get caught if he kept his mouth shut"), the message is clear.
Take a look at some of the best examples:
Only a foolish person would talk to strangers about important military plans. The king of foolish people, "Joe Dope," was the star of many military posters.