The Greek Line, formally known as the General Steam Navigation Company of Greece, was a passenger ship line that operated from 1939 to 1975. The Greek Line was owned by the Ormos Shipping Company. The line operated transatlantic and short-to-long distance voyages. The company later began operating leisure cruises as the jet age replaced passenger ships as the means of transportation across the Atlantic Ocean.
Except for one ship, the Olympia, all of the ships that the Greek Line operated were second-hand purchases. One of the line's former ships, the Queen Anna Maria, became the Carnivale. The Carnivale was the second ship to sail for the then newly-formed Carnival Cruise Lines, which today is one of the largest cruise lines in the world.
None of the Greek Line's former ships are in operation. The last ship was retired and sold for scrap in spring 2009 see Wikipedia (https://en.wikipedia.org/wiki/Greek_Line)
image taken from Facebook ....note its in British currency!
According to this site (http://www.simplonpc.co.uk/GreekLinePCs.html), the Greek line ships played a role in the post-war wave of emigration from countries devastated in the second world war, in particular Germany, but probably also France and French North Africa (the Dutch market was already well covered by local lines) to the "white commonwealth" countries, especially Australia.
In the early fifties, there were still export and currency exchange controls on local currencies. It is quite possible that the denomination on this token was thought of as an Australian florin, all the more so because of Australia's preference for florins over half crowns in pre-decimal days.