The Indus Dictionary Project
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.
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.
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 east. Peter Dekker has some photographs of Tibetan's using self bows¹. 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.
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.
1. Photographs of Tibetan archers: Peter Dekker, 2014: Fe Doro: http://www.manchuarchery.org/photographs-tibetan-archers: Accessed: 31 January, 2019.