This is the ideograph for a man, which is placed between a pictograph of two shafts. I imagine that the man is pulling a handcart. Hence, Mahadevan's sign number 212 is an ideograph for the verb to haul.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-3 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 2: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 212: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.