This is the noun area with the addition of a third dimension. Hence, it is an ideograph for a cube. A cuboid, similar to the Mesopotamian gur, was used to measure volume.
Mahadevan's sign number 149 does not have unit markings. It therefore, becomes an ideograph for a procedure. It is the noun method or way.
This Indus sign shares a common root with the Chinese character dí 由.
Illustrative Text References:
Mohenjo-daro: Seal: M-35 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 19: Collections in India: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-1739 a: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 37: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Comment:
In modern Chinese 由 is more often pronounced yóu, which means reason or cause.
Image Credit:
Indus Script Sign Number 249: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.