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 five Indus units tall.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-1731 a: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 34: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Comment:
In inscription M-1731, Mahadevan's sign number 1159 is repeated, which gives us a double door or a pair of gates.
Image Credit:
Indus Script Sign Number 1159: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.