This is the flag of the Antarctic Treaty used by the permanent Antarctic Treaty Secretariat (ATS); its headquarters are in Buenos Aires. This flag can also be used by the countries which joined the treaty and is hoisted the annual CPAT meetings (28 states with statute of consultative parties and 17 more as non-consultative). The ATS has international legal status.
The use of this flag results from Article 7 of headquarters agreement negotiated with Argentina. The flag is derived from the ATS emblem adopted in Warsaw (25th CPAT, 10-20 September 2002) by Decision Number 2 of 20 September 2002. This flag shows the outlined map of the Antarctic continent in white on a navy blue (Pantone 295C) background with the main latitude and longitudinal lines superposed.
There's now solid evidence that this is adopted as the "Emblem" (and flag) "of the Antarctic" by the Treaty Organization; it is not just the Organization's own emblem/flag.
At the intiative of the United Kingdom, Working Paper (XXV ATCM/WP5), Decision 2 (2002) was adopted:
Emblem of the Antarctic Treaty
Desiring to provide a clear identity to the work of the ATCM and its Secretariat;
Conscious that there exists a design traditionally employed by the Antarctic Treaty parties to identify their work, but that the design has no formal status;
Believing that the adoption of such a design would enhance presentationally the work of the ATCM and its Secretariat when located in Buenos Aires;
That the design annexed to this Decision shall constitute the formal emblem of the Antarctic Treaty.
That it may be used by:
The Secretariat of the Antarctic Treaty;
The host state of the ATCM or Special ATCM in the period of preparation for and during a Consultative Meeting;
By any other Consultative Party when hosting other meetings under the auspices of the Antarctic Treaty of its Environmental Protocol;
By others with the authority of the ATCM.
That the design shall be shown on the official Reports of the ATCM and may be employed at the premises of the Antarctic Treaty Secretariat, on its official means of transport, as well as on stationary, electronic communications, reports, flags, signs, etc.
The flag of Antarctic. RGB : 000-051-102. CMYK : 100-56-0-34. Pantone: 295C. Source: Michel Sicard (SFV)
There is a pdf of the actual emblem online. I wonder if the lines extend all the way to the edges of the actual flag, though, as it is not quite possibleto see in the Swedish photograph, which incidentally, is either the wrong way around or upside-down.
It seems to be 3:5 with the 60° and 120° meridians doubling as diagonals. The stripes on the flag (as seen in the two photos online at the 28th ATCM in Stockholm from 6 to 17 June 2005) are much thicker than those in the official document on line.
Please note, this is the same emblem which appears in the above referenced source as Annex B and is thus the official or "formal emblem" of the ATCM, as the decision states. There are differences, incorporating some artistic licence, however, in the manner in which the emblem is used, noticeably in the black and white version which appears on many ATCM reports and on the web site of the ATS itself.