I was most interested to read the piece from George Wingfield about the MN Badge, and wonder I could add some further information.
A uniform for the Mercantile Marine (later the Merchant Navy) was introduced by The Mercantile Marine (Uniform) Order of 4 September 1918. The Order noted that it was expedient that a "National Standard Uniform" should be adopted.
In July 1918 King George V had expressed his desire to recognize the war service of the Mercantile Marine and it has been generally thought that a specific change of title was granted to reflect this, although the actual point of change seems to lie in the creation of the Prince of Wales as Master of the Merchant Navy and Fishing Fleets in February 1928 (this office being held by successive monarchs to the present day). The Admiralty announcement noted that this brought them into line with the "other great Services of the Empire" by having a member of the Royal Family as their titular Head, and also in recognition of the service which the Merchant Navy and Fishing Fleets had rendered for many centuries, both in peace and in war.
Despite the Order of September 1918 the situation of a lack of recognizable uniform continued into the War of 1939-1945 and it was decided to issue all personnel of the Merchant Navy with a badge to indicate to the public that the wearer was engaged in vital war work. The small MN badge, in silver, was introduced from January 1940 to be worn in the lapel of a jacket.
