This is an ideograph for the adjective weekly. A sequence of seven points of light (shorter lines) is set within a cylinder. Hence, we have a group of seven days, in other words a week.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-1775 a: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 47: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 2011: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.