The Indus Dictionary Project
This is a pictograph of a single-pronged vajra, which was a type of throwing weapon.
Harappa: Tablet: H-183 A: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 210: Collections in India: Suomalainen Tiedeakatemia.
There are two tablets, H-183 and H-184 which appear to carry the same inscription and motif. It is of interest that the inscription incorporates a pictograph of a measuring rod with a length of six units. Presumably, this was used to measure the distance thrown. It therefore, seems likely that the tablets were tokens for entry to a tournament.
Indus Script Sign Number 268: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.