I have posted a fair few Propaganda posters on this blog, virtually half of them warning people not to speak idle words, showing what can happen if they do so. This by the way of a comic strip pretty much tells us a story of what can happen. Not typical for posters but one assumes people stopped and read the thing or were handed to them in leaflets to read.
Cliffs of the comic: Geezer tells waiter when he leaves on a ship, someone overheard and tells someone else, that person tell spy and they inform enemy who bomb ship.
Was idle chit chat such a huge problem or was it just paranoia?