The 'Keep Calm and Carry On' poster was designed by the Ministry of Information between 27th June and 6th July 1939.
Almost 2.5 million posters were printed from 23rd August upto the outbreak of WWII on 3rd September 1939, however they werent sanctioned for public display, and were largely forgotten.
Then, in 2000, the owners of a second hand bookshop in Alnwick discovered an original copy of one of the posters in a batch of books. They framed it and put it behind the tills. It began to gain interest, so the owners started selling copies. Shortly afterwards, it ballooned into the world-wide phenomenon it currently is, with the phrase being adapted for all sorts of things...
So to the cache.....N54 AB.CDE W001 FG.HJK where...
A = Teacher
B= Sergeant
C = Cowboy - Jack
D = Abroad - Henry - Teacher
E = Constable
F = Nurse
G = Cruising
H = Spying
J = Columbus - Dick - Regardless
K = Camping - Doctor