The Indus Dictionary Project
An equilateral triangle is used to illustrate the concept of rotation. The triangle rotates around a fixed central point.
For image credits, please see below.
Indus Script Signs with Numbers: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.
Indus Script Signs without Numbers: Lynn Fawcett, 2017 - 2018.