The Indus Dictionary Project
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.
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.
In Indus inscription H-10, Mahadevan's sign number 1018 is combined with the the verb brush to form an ideograph for the verb oil. It therefore seems likely that oil was transported in size four containers.
This usage can be linked to Chinese. The Chinese character yóu 油 is the noun oil, and the expression 油油 means oily.
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.