This ideograph is the verb to obscure or to hide.
Illustrative Text Reference:
Harappa: Copper Model of a Vehicle: Stuart Piggott, 1970: Copper-Models in the Indus Civilization: Fig. 1: The Journal of the Royal Asiatic Society of Great Britain and Ireland: Page 201.
Image Credit:
Indus Script Sign Number 137: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.