Andean pictographic writing, once considered the creation of foreign missionaries, is now recognized as a series of locally developed scripts that emerged after contact with alphabetic writing. However, the role of stylistic variation within the Andean pictographic scripts is little understood, nor has the rebus-based glottography of the system’s phonetic signs been fully studied. This article examines the Koati variant of Andean pictographic script from Bolivia’s Island of the Moon, based in part on a newly found pictographic manuscript preserved on animal hides in Harvard University’s Peabody Museum. It analyzes how script styles in the Titicaca area correspond to regional groups and explores the nature of rebus signs in the Koati variant, identifying the principles underlying successful homonymic equivalences. Many of the characters in Andean pictographic writing appear to draw from a repository of Indigenous visual signs that predate the Spanish invasion; research into the emergent pictorial scripts of Peru and Bolivia may provide insights into the meaning of visual signs in other forms of Andean inscription, such as ceramics and khipus.