The Sanskrit root meaning to be born begins with this letter, and it is one of the most productive roots in the language. As the final member of a compound it forms adjectives meaning born of, produced from or arising in, so an enormous class of descriptive terms ends in this consonant: the lotus is the water-born, a large part of the vocabulary of caste and lineage is built on the same root, and so are the words for birth, kinship and the cycle of rebirth that runs through the religious literature of the subcontinent.
A second high-frequency root beginning with this letter is the one meaning to know, and it supplies the noun for knowledge that names one of the classical paths in Indian religious thought. That word is written with a conjunct of this letter and the palatal nasal, a cluster whose pronunciation drifted a long way from its spelling in the later languages and whose written form in several descendant scripts fused into a ligature that no longer shows either of its parts. In Brahmi the two components are still separately visible in the conjunct, which is one of the small ways in which the parent script is easier to read than its children.
For a reader of the earliest inscriptions the letter is common in a specific place: personal names. The donative records that make up most of the surviving early Brahmi name their donors, and a great many Indian personal names are compounds built on the roots this letter opens, so the sign recurs in exactly the part of the text that varies from inscription to inscription. That is useful, because a decipherer works from the constant part of a formula and tests the reading against the variable part, and names are the variable part.