This symbol shares a common root with the Classical Yi verb zop. The definition of zop is to rebalance a load.
In ideographic terms there is a pictograph of three packs, which represents the three stages of the procedure. Namely, unloading the goods, redistributing the weight, and reloading the goods.
Illustrative Text References:
Mohenjo-daro: Seal: M-99 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 37: Collections in India: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-324 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 81: Collections in India: Suomalainen Tiedeakatemia.
Comment:
In some of the Indus inscriptions, this sign is used to describe designated loading and unloading places. An example is inscription M-99, in which the town crier announces the arrival or departure of caravans.
Image Credit:
Indus Script Sign Number 415: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.