In this ideograph, the glyph denoting the end of an area is combined with a pictograph of half the sun. It is the end of the domain of the sun, in other words the sunset. In context, the noun evening is often a good translation.
Illustrative Text Reference:
Harappa: Seal: H-1657 A (NB. image H-1657 A is a mirror image of Mahadevan's sign number 301): Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 231: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 301: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.