This is a pictograph of a mountain range. It is the singular noun mountain or the plural noun mountains.
The symbol shares a common root with the Chinese character shān 山.
Illustrative Text Reference:
Harappa: Tablet: H-187 A: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 210: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 1459: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.