The Indus Dictionary Project
In this section, the little roof shape that you can see on the left is used to represent the sky. This ideograph for sky can only be found within composite characters in the extant Indus inscriptions. However, a similar symbol for sky does exist as a stand alone character in Naxi Dongba¹.
For image credits, please see below.
Indus Script Sign with a Number: 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 - 2019.
1. A bitmap of the Naxi Dongba symbol for sky can be seen at: http://www.zmnsoft.com/edongba/En/FontDemo.html: Accessed: 16 February 2021.