I had seen this motto in Japan when they were having a British themed sale at an import shop.
Apparently this motto was thought up during WWII as a way to "cheer" on the Brits.
Before they could use it though, the war ended, so most of these posters were destroyed.
Then 60 years later, a bookseller named Stuart Manley, found this among some old books. And even more recently, more posters were found and auctioned.
The company, Keep Calm and Carry On was able to purchase one and used it for posters, t-shirts and other knick-knacks.
According to some, the motto sends a comforting and reassuring message.
I think it's pretty cool.