The Indus Dictionary Project
This is a pictograph of a stream flowing into a river. There is a point of light at the south cardinal point, and points of darkness at each of the other cardinal points. Hence, this symbol makes specific reference to a tributary located to the south.
Harappa: Incised Tablet: H-325 A: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 226: Collections in India: Suomalainen Tiedeakatemia.
There is only one extant example of this symbol.
Note the alignment, in this Indus sign, of the point of light at south with the right-hand side of the point of darkness at west. The position may have been chosen to avoid confusion with the symbol for dusk.
Southern Tributary: Lynn Fawcett, 2020.
Indus Script Sign Number 103: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.