In this Indus sign, two water symbols are rotated through 90 degrees to give the idea of a large volume of flowing water.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-1923 c: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 83: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Flowing Water: Lynn Fawcett, 2020.