This is a pictograph of a man with a bow and arrow. It shares a common root with the Chinese noun yí 夷, meaning foreigner.
Illustrative Text References:
Harappa: Seal: H-10 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 167: Collections in India: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-626 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 7: Collections in Pakistan: Suomalainen Tiedeakatemia.
Comments:
The bow shape indicates that it is a self bow.
Although Mahadevan's sign number 28 can be read as foreigner in the Indus inscriptions, it is worth remembering that the sign may have referred to a specific place, the associated region, and the people who came from that region.
Xu Shen's etymology for yí 夷 states that such people came from the east¹. Peter Dekker has some photographs of Tibetan's using self bows². Tibet is to the east of the Indus Valley. It is therefore, possible that the symbol refers to people from the area that we now know as Tibet.
Image Credit:
Indus Script Sign Number 28: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.
Notes:
1. Xu Shen, 121: Radical number 389; Character number 6581: Shuowen Jiezi (Explaining and Analyzing Characters): http://www.shuowenjiezi.com/: Accessed: 1 July 2020.
2. Photographs of Tibetan archers: Peter Dekker, 2014: Fe Doro: http://www.manchuarchery.org/photographs-tibetan-archers: Accessed: 31 January, 2019.