Megalithic graffiti symbols

From the longer Wikipedia page 
Megalithic markings, megalithic graffiti marks, megalithic symbols or non-Brahmi symbols are markings found on mostly potsherds found in Central India, South India and Sri Lanka during the Megalithic Iron Age period. A number of scholars have tried to decipher the symbols since 1878, and currently there is no consensus as to whether they constitute undeciphered writing or graffiti or symbols without any syllabic or alphabetic meaning.
An article here
Category:Undeciphered writing systems