The walls have ears
This advertisement encouraged Canadians to be particularly careful about what they said in hotels, for it was always possible that an enemy agent might be listening.
Canada, Director of Information, Souvenez-Vous que les Murs ont des Oreilles, n.d. [1941?]
War, Memory and Popular Culture Archives - The University of Western Ontario - London, Ontario
card, 10.1cm x 10.1cm