This is the noun midpoint where part of the right hand triangle is replaced by a semi-circle and some rays of light. Reading from right to left: midday is preceded by rays of light emanating from the sun. Hence, this symbol is an ideograph for morning rays.
Illustrative Text Reference:
Dholavira: Seal: SI. Number: 127: Acc. Number: 25871 (NB. The photograph is of the seal. Therefore, the inscription would be the mirrored image of that seen in the photograph.): R.S. Bisht, 2015: 8.2.3 Details of Individual Seals: Excavations at Dholavira (1989-90 to 2004-2005), p. 288: https://www.scribd.com/document/262316120/Excavations-at-Dholavifra-1989-2005-RS-Bisht-2015: Accessed: 12 November, 2018.
Image Credit:
Morning Rays: Lynn Fawcett, 2018.