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 four spaces between the vertical bars, which gives us a size four cage.
Illustrative Text Reference:
Harappa: Tablet incised: H-2059 A: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 281: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Comment:
It is possible that H-2059 was a permit for a cart, with a specified load, to enter the city.
Image Credit:
Indus Script Sign Number 1140: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.