The Indus Dictionary Project
This is the ideograph for sky combined with the noun summer. Hence the translation is summer sky.
Kalibangan: Seal: K-29 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 304: Collections in India: Suomalainen Tiedeakatemia.
There is only one extant example of this Indus sign. It is therefore, unfortunate that seal K-29 is broken, and we do not have access to the full inscription.
I have not been able to trace the etymology for the use of the little roof shape to represent the sky. One possibilty is that it is related to the Chinese character bā 八. The Unihan definition for this character includes: 'all around', which could be taken to mean atmosphere. However, I stress that this interpretation is mere conjecture.
Indus Script Sign Number 92: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.