In this symbol, the noun trade route has the dot of emptiness placed at its centre. In other words, the route is strange or unfamiliar. Hence, Mahadevan's sign number 397 translates as 'new trade route'.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-1684 a: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 14: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 397: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.