In this symbol, the glyph denoting the beginning of an area is combined with a point of light. The point of light marks the transition from night to day at the summer solstice, when the sun rises in the north-east. For the northern hemisphere, this is the most northerly, and also the earliest sunrise. Hence, Mahadevan's sign number 288 is an ideograph for the noun first light.
Illustrative Text References:
Mohenjo-daro: Seal: M-677 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 35: Collections in Pakistan: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-1316 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 168: Collections in Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 288: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.