This is a pictograph of a pen, to which bars have been added across the top. In other words, it is a cage. In this instance, there are five spaces between the vertical bars, which gives us a size
Illustrative Text Reference:
Mohenjo-daro: Seal: M-372 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 93: Collections in India: Suomalainen Tiedeakatemia.
Indus Script Sign Number 1438 (Cage Size 5): List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of