I recently purchased this poster to hang in my apartment. It is so fitting for my life I had to have it. I'll post a picture of it once it is up.
These propaganda posters were originally commissioned by the British Government's Ministry of Information before WWII when the UK was preparing for the inevitable war with Germany. The posters were never officially issued, and were forgotton until one turned up at auction 50 years later.
You can find the posters at http://www.keepcalmandcarryon.com/, or multiple vendors on http://www.etsy.com/.