This composite character is the noun goods with the addition of two counting rods (the numeral two). The numeral indicates the relative size of the shipment. Hence, Mahadevan's sign number 344 is an ideograph for a medium-sized shipment of goods.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-754 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 58: Collections in Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 344: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.