This Humanist Party "franchise" seems to be all over the world, or at least aiming to. From what I could gather up to now their ideology is a brew of trendy New Age concepts; in Portugal they are apparently envolved in things so varied as immigrant support, promotion of occultism and animal rights. António Martins, 24 August 2003
Speculating a bit on the symbol, it could refer to the math symbol of infinity, also present in other flags. Jorge Candeias, 3 August 1999
The political orientation of the HP is roughly "left" (at least they claim so). It's interesting that the HP is a really international party: originally founded in Argentina, it has branches now in more than 70 countries all over the world (about 30 of them with websites).
The basis of the political program ("New Humanism") are the publications by the Argentine founder of the movement, "Silo" (a.k.a. Mario Luis Rodríguez Cobos), including the Orange Book (Libro naranja). The whole movement seems to be rather centralistic; there exists the opinion, that the HPs all over the world are more a kind of a religious sect led by Silo than a political party. The followers of Silo are also called Siloists.
Regarding the symbols of the party: the colour orange is prominently displayed, for instance on websites, but also participants of the 2001 May demos in Munich wore orange clothes, were flying orange ribbons and orange flags. Beside the colour (also appearing in the above-mentioned Orange Book), the sign of infinity in form of a "Moebius ribbon" (in different variants) is the logo of the whole movement (also on the flags).
However, what makes this party (or international movement) problematic for vexillologists, is the consistent tendency not to answer any requests regarding their flag (even more than usual for German parties). I contacted the German HP at least 10 times (per e-mail or fax) until I got an answer. I wrote e-mails to the different branches of the party, especially to Argentina, and only got sufficient answers from Switzerland (16 January 2002), Basque Country (18 February 2002), and Italy (23 January 2002); not really sufficient answer from Germany; and 23 countries (including Argentina) did not answer.
So I can only state, that the HP movement uses as symbols the orange colour and the Moebius ribbon. These are also shown on flags in slightly different constellations in different countries.
The Moebius ribbon symbolizes the infinity, therefore also the infinite possibilities of human beings. Furthermore it symbolizes the continuity between the personal sphere and the social sphere, and the need for a coherence in social and personal change. The orange colour symbolizes "help and solidarity."