This was the collective name used by a body of designers who were used by Pepys. The initials stand for Marine Jockey Commisions Ltd.
From a leaflet inside Horse Racing To-night, one of their games;
This amazing organisation, which was started in a Prisoner of War Camp by men of the Merchant Navy, served, during many dark war years, to brighten the lives of thousands of fellow prisoners, and, incidentally, at the same time to raise over 3,000 pounds for the British Red Cross. It also helped to give extra food to sick prisoners in the Camp Hospital, and did many other charitable deeds.
Why 'Commission'? Thereby hangs a tale! The originators naturally bestowed on their invention the name of Marine Jockey Club, but the Nazis, in their supreme egotism, would not tolerate any Club, as the Nazi Party was the only organised body allowed in the Reich. The inventors had nimble minds and changed the offending word to 'Commission'. Thus were the dull and humourless Nazis appeased and all was well.