This is a pictograph of an arch. Hence, it is the noun archway.
Illustrative Text Reference:
Kalibangan: Seal impression: K-89 A: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 318: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 2103: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.