The writing on the pot is in Tamil Brahmi, a writing system that only fairly recently has come to be well understood. It says: n̪a:kan uɾal, Old Tamil for “Naakan’s (pot with) toddy-sap”. In modern Tamil writing this would be: நாகன் உறல். As the article points out, the fact that a poor toddy-tapper would write his name on a pot is indicative of mass literacy at the time.
As Doc Rock points out in the comments, the pot does not prove mass literacy, but it’s certainly indicative of it, and it makes me curious to learn more about the society. Other interesting points: the article “is not by reporters; it is right from the horse’s mouth. The authors are S. Rajagopal, retired senior archaeologist with the Tamil Nadu State Department of Archaeology and Iravatham Mahadevan, an eminent student of early Indian writing and leading authority on Tamil Brahmi… This is like having a newspaper article on physics written by Stephen Hawking.” And one of the commenters in the thread is a native speaker of Tamil; not quite as unusual as the speaker of Circassian/Kabardian who turned up in my Chakobsa thread, but an indication of the worldwide reach of the internet.