Mahadevan's sign number 404 is a composite character. The verb to trade is surrounded by four points of light. A speck of light denotes that something is true. It follows that a point of light at each of the cardinal points is an ideograph for the adverb everywhere. Therefore, sign number 404 means to trade or to sell everywhere.
Illustrative Text References:
Mohenjo-daro: Seal: M-234 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 58: Collections in India: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-626 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 7: Collections in Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 404: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.