The Indus script represents logo-syllabic writing. This means that it does not constitute such a closed system of single-valued graphemes as the syllabic and alphabetic scripts, which could be cracked as wholes. Rather, individual signs may be interpreted one by one, and many of the graphemes are likely to remain eternal mysteries.
The interpretations presented above, few in number but cross-checked, suggest that the Indus script was essentially similar to the other pictographic scripts created before the middle of the third millennium B.C., that the language of the Indus people was Dravidian, and that they professed a religion that was genetically related to the religions of both the ancient West Asia and the later India.
The Harappan religion emerging from these interpretations is in an interesting way reflected in the Indus pictograms. As iconic signs making use of the picture puzzle (or rebus) principle, they can simultaneously communicate two separate messages, one pictorial, one phonetic. It seems to me that the creators of the script were at pains to invent such iconic symbols that the two messages would be in harmony with each other. Witness the 'roofed fish' (pictorial message) as the rebus for the 'black star' (phonetic message), both symbols for the deified dark planet Saturn, conceived as riding the slow-creeping tortoise.
[Originally published as Parpola, Asko (1988) Religion reflected in the iconic signs of the Indus script: penetrating into long-forgotten picto+graphic messages. Visible Religion 6: pp. 114-135.]