Gary Urton has suggested that the quipus used a binary system which could record phonological or logographic data.
At the start of the game, Carmen steals a rare Franco-Italian edition of The Travels of Marco Polo (which conveniently has the title written on the cover in English) and, as the game progresses, she goes on to steal a Māori wood carving, Incan Quipus and other seemingly random items.