This is the symbol for area with the addition of a line which represents a third dimension. Hence, it is an ideograph for a cuboid. A cuboid was a measure of capacity. It can be likened to the Mesopotamian gur. In this instance, the cuboid is divided into four Indus units.
Illustrative Text References:
Harappa: Seal: H-10 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 167: Collections in India: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal without a motif: M-356 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 89: Collections in India: Suomalainen Tiedeakatemia.
Comments:
In Mesopotamia a gur was used to measure the volume of oil. This also appears to have been the case in the Indus Valley Civilisation because in Indus inscription H-10, the cuboid of Mahadevan's sign number 1018 is combined with the the verb to brush, to form an ideograph for the verb to grease.
Image Credit:
Indus Script Sign Number 1018: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.