You have probably more than once seen the posters printed with the slogan "Keep Calm and Carry On" and/or variations of it.

I had no idea of the slogan's history, but it turns out it origins from the Second World War to instill peace in the British people and was re-discovered in 2000 when one of these propaganda war posters was found in a box by secondhand bookshop Barter Books.

Via Holy Kow.