The Indus script that labels these seals has never been deciphered, so the horned seated figure on seal M-304 and its kin cannot be read against a text that would say who or what it depicts. The proto-Shiva reading popularized in early twentieth century scholarship rests on visual resemblance to later Hindu iconography (the seated posture, the horns, the surrounding animals), not on any legible caption, and Srinivasan's own iconological re-assessment finds the identification unsupported by the seal's own details.
What would resolve this A decipherment of the Indus script that survives scholarly scrutiny, or an independently datable bilingual inscription pairing Indus signs with a known language, would let the seals be read on their own terms rather than through later Vedic or Hindu iconography projected backward onto them.
OpenIndus Valley archaeology, epigraphy and comparative iconographyDoris Meth Srinivasan, The So-Called Proto-Siva Seal from Mohenjo-Daro: An Iconological Assessment