The name Tamil itself ends in this sound, which is as compact a statement as could be wanted of how closely the letter is identified with the language. Speakers describe it as the sound that marks their speech out from its neighbours, and it is difficult for outsiders to produce: the tongue tip is drawn back towards the roof of the mouth without making contact, so the sound is neither a lateral nor an r though it has something of both, and no Indo-Aryan language has anything like it.
The letter has no counterpart in the alphabets of the north, and its presence in an inscription is therefore direct evidence of where the text was cut. That is unusual. Most of the evidence a palaeographer works with is a matter of degree, the shape of a common letter compared against dated examples, and a sign that simply is not available elsewhere gives a much harder answer.
It is written in modern Tamil and in Malayalam, which shares the sound, and it survives in Malayalam and Tamil alike as one of the letters that mark the southern branch of the family. Sanskrit and Prakrit texts have no use for it at any period, and it is one of the three consonants that Tamil-Brahmi added at the end of the inherited order rather than adapting an existing letter to serve.