In this Indus sign, one standard, of four units, is placed directly below another of the same size. Hence, it is an ideograph for an equivalent measure.
Illustrative Text References:
Mohenjo-daro: Seal: M-28 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 16: Collections in India: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-114 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 40: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 1494: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.