The seal was uncovered in 1928 or 1929, in Block 1, Southern Portion of the DK-G Area of Mohenjo-daro, at a depth of 3.9 meters below the surface. Ernest Mackay, who directed the excavations at Mohenjo-daro, dated the seal to the Intermediate I Period (now considered to fall around 2350–2000 BCE) in his 1937–1938 report in which the seal is numbered 420, giving it its alternate name.
The first description and analysis of the seal's iconography was that of the archaeologist John Marshall who had served as the Director-General of the Archaeological Survey of India and led the excavations of the Indus Valley sites. In addition to the general features of the seal described above, he also saw the central figure as a male deity as three-faced, with a possible fourth face towards the back and, as ithyphallic, while conceding that what appeared to be the exposed phallus could instead be a tassel hanging from the waistband. In a 1928–29 publication, Marshall summarized his reasons for the identification as follows:
My reasons for the identification are four. In the first place the figure has three faces and that Siva was portrayed with three as well as with more usual five faces, there are abundant examples to prove. Secondly, the head is crowned with the horns of a bull and the trisula are characteristic emblems of Siva. Thirdly, the figure is in a typical yoga attitude, and Siva [sic] was and still is, regarded as a mahayogi—the prince of Yogis. Fourthly, he is surrounded by animals, and Siva is par excellence the "Lord of Animals" (Pasupati)—of the wild animals of the jungle, according to the Vedic meaning of the word pashu, no less than that of domesticated cattle.
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According to my understanding, John Marshall might have rightly guessed a possible fourth face towards the back, but he wrongly guessed it as ithyphallic. I think, he forgot to understand that there could be a fourth face, towards backside, which cannot be visible to the viewers, as it is a Two dimensional image.
Let us remember the 4 sided Ashoka pillar, featuring four lions back-to-back on a drum base.
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Similarly, the seal that was found in Mohenjo-daro might be having 4 faces, the fourth face remaining invisible on the back side.
This might not be Proto-Shiva, but might be indicating Agni, who was mentioned a having 4 eyes in Rig Veda 1.31.13, indicating the DIVINE Agni is watching all directions.
त्वमग्ने यज्यवे पायुरन्तरोऽनिषङ्गाय चतुरक्ष इध्यसे । यो रातहव्योऽवृकाय धायसे कीरेश्चिन्मन्त्रं मनसा वनोषि तम् ॥
tvam agne yajyave pāyur antaro 'niṣaṅgāya caturakṣa idhyase | yo rātahavyo 'vṛkāya dhāyase kīreś cin mantram manasā vanoṣi tam ||You, Agni, are kindled as intimate protector, four-eyed, for the worshipful one who lacks even a quiver, you who, with the bestowed oblation, for nourishment safe from wolves even for the weak, win this mental spell (for him) with your mind.
