"Keep calm and carry on!"
(or, as one of our local Indian restaurants has it, keep calm and curry on).
Of course, everyone knows that the "Keep calm" phrase originated in (don't mention) the war, but did you know that, quoting Wikipedia, "the poster was hardly ever publicly displayed and was little known until a copy was rediscovered in 2000 at Barter Books, a bookshop in Alnwick".
