While we are trying to figure out if Harappans wrote in proto-Brahmi, here is a interesting story about something that was written in Tamil using Brahmi script. An Italian archaeological mission to Oman found a potsherd in 2006 in the Khor Rori area, but they could not make out what was written on it. They displayed it at a workshop in Kerala and our folks were able to read what was written on it.
The script “nantai kiran,” signifying a personal name, has two components, Dr. Rajan said. The first part “[n] antai” is an honorific suffix to the name of an elderly person. For instance, “kulantai-campan,” “antai asutan,” “korrantai” and so on found in Tamil-Brahmi inscriptions could be cited. The second component “Kiran” also stands for a personal name. More than 20 poets of the Tamil Sangam age [circa third century BCE to third century CE] have “kiran” as part of their personal names. “Thus, the broken piece of the pot carries the personal name of an important trader who commanded a high regard in the trading community,” Dr. Rajan argued. [Potsherd with Tamil-Brahmi script found in Oman]
The potsherd is dated to around the first century CE. Previously Tamil-Brahmi texts have been found in Berenike and Quseir al-Qadim in Egypt and this is the first time such text has been found in the Arabian peninsula. This discovery of the text itself is not shocking for there exists enough historical evidence for trade for Indian Ocean trade dating to that period.
While there is still controversy over how old Tamil-Brahmi is, texts have been found in various places in South India, like Adichanallur. It also has been found as far away as Thailand