The Antarctic is a huge continent, about as large as 1.5 times the Europe, almost totally covered by ice. Just to give an idea of the temperature over there, on the central table-land the average temperature is under -50 °C (-60 F), while on the coast-line it's "higher", with about 0 °C (30 F) in the hottest months of the summer! The lowest temperature was measured in 1983 in the Russian base of Vostok: -89.6 °C (-129.3 F)!
From the legal point of view, the Antarctic is a land that does not belong to any State; in the past there were some claims, but they were settled with the "Antarctic Treaty" that regulates the presence of the States on the continent. It was signed in Washington on December the 1st, 1959 among 12 of the Countries attending the International Year for Geophysics (1957-58) and came into force in 1961. The idea behind this treaty is to promote a pacific use of the continent, to suspent any claim and to forbid any military activity with the aim of saving the unique flora and fauna for the future.
All the Countries supporting the treaty have the right to access the full continent and to make pacific activities in the whole Antarctic with no borders. The personnel working in the Antarctic is subject to the law of its origin Country.
And this is true also for the plates! For this reason there is not only one license plate for the full Antarctic, but every base has got its own plates, according to its origin.
From certain sources, I found out that the vehicles in use in the Italian bases haven't got any plate at all. The plates showed below are used on the vehicles of other Countries (United States and France: many thanks to Giancarlo Raposo and to Alessandro Libanore for these pictures!).