with the Indus script, there is no scholarly consensus on the meaning of these non-Brahmi symbols. Some scholars, such as the anthropologist Gregory Possehl, have argued that the non-Brahmi graffiti symbols are a survival and development of the Indus script into and during the 1st millennium BCE. In 1960, archaeologist B. B. Lal found that a majority of the megalithic symbols he had surveyed were identifiably shared with the Indus script, concluding that there was a commonness of culture between the Indus Valley Civilisation and the later Megalithic period. Similarly, Indian epigraphist Iravatham Mahadevan has argued that sequences of Megalithic graffiti symbols have been found in the same order as those on comparable Harappan inscriptions and that this is evidence that language used by the Iron Age people of south India was related to or identical with that of the late Harappans. Characteristics The characters are largely pictorial, depicting objects found in the ancient world generally, found locally in Harappan culture, or derived from the natural world. However, many abstract signs have also been identified. Some signs are compounds of simpler pictorial signs, while others are not known to occur in isolation, being known only to occur as components of more complex signs. Some signs resemble tally marks and are often interpreted as early numerals. Number and frequency The number of principal signs is over 400, which is considered too large a number for each character to be a phonogram, and so the script is generally believed to be logo-syllabic. The precise total number of signs is uncertain, as there is disagreement concerning whether particular signs are distinct or variants of the same sign. In the 1970s, the Indian epigrapher Iravatham Mahadevan published a corpus and concordance of Indus inscriptions listing 419 distinct signs in specific patterns. However, in 2015, the archaeologist and epigrapher Bryan Wells estimated that were around 694 distinct signs. Of the signs identified by Mahadevan, 113 are hapax legomena, 47 occur only twice, and 59 occur fewer than five times. Just 67 signs account for 80 percent of usage across the corpus of Indus symbols. The most frequently used sign is the "jar" sign, identified by Parpola as 'sign 311'. Writing direction Most scholars agree that the Indus script was generally read from right to left, however, some exceptions wherein the script is written left to right or in a boustrophedon mode are also known. Although