A paper in Science aims to support the thesis that the Indus script represents a language, rather than a non-linguistic symbolic system as claimed by Steve Farmer.
Farmer, Sproat and Witzel completely reject this paper (pdf) in a quick response. I tend to agree with them. I didn't really see any strong evidence that conditional entropy can distinguish between linguistic and non-linguistic symbol systems in the Science paper, and the brevity of the Indus Script inscriptions argues strongly against the linguistic hypothesis.
(Another technical refutation at the Language Log)
Entropic Evidence for Linguistic Structure in the Indus Script
Rajesh P. N. Rao et al.
The script of the ancient Indus civilization remains undeciphered. The hypothesis that the script encodes language has recently been questioned. Here, we present evidence for the linguistic hypothesis by showing that the script’s conditional entropy is closer to those of natural languages than various types of nonlinguistic systems.