Mahadevan's sign number 2422 is the noun city with the noun cart load placed at its centre. Hence, it is an ideograph for a market town.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-655 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 27: Collections in Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 2422: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.