This is a pictograph of a door or gate. The Indus symbol for a door or a gate is always two Indus units wide. This one is four Indus units tall.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-980 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 95: Collections in Pakistan: Suomalainen Tiedeakatemia.
Comment:
In inscription M-980, Mahadevan's sign number 1542 is repeated, which gives us a double door or a pair of gates.
Image Credit:
Indus Script Sign Number 1542: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.