You may be familiar with the classic English poster, Keep Calm and Carry On, which was produced by the UK government in 1939 during the beginning of the WW2. It was intended to raise the morale of the British public in the event of invasion but it had only limited distribution. The poster was rediscovered in 2000 and has been re-issued by a number of private companies, and used as the theme for a range of products.
I’ve seen many variations in the past several years, but this one may be my favorite yet. You can find it on Etsy.