As Iravatham Mahadevan points out, archaeological evidence makes it inconceivable that IVC's large, well-administered and sophisticated trading society would have functioned without effective long-distance communication. Unlike the clay tablets of Mesopotamia, no written records were discovered from Indus Valley sites except seals. The people of IVC might have written on cotton cloth, leaves, bark or hide which would have decayed by now, leaving no trace.
Iravatham Mahadevan
Ancient Indus questions answered by Iravatham Mahadevan, Indus Research Centre, Chennai. Iravatham Mahadevan was India's leading expert on the ancient Indus script, is author of The Indus Script: Texts, Concordance and Tables. He has numerous articles on this website, as well as the essays The Indus Script and The Arrow Sign in the Indus Script.