This composite character is the noun trade combined with a stylised right hand (the hand is shown in profile). In most people the right hand is the dominant hand. The dominant hand is the most skilful hand and is associated with the performance of tasks. Hence, Mahadevan's sign number 405 is the noun trade assistant.
Illustrative Text Reference:
Mohenjo-daro: Tablet incised copper: M-605 B: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 152: Collections in India: Suomalainen Tiedeakatemia.
Comments:
There is only one extant example of this Indus sign.
The inscription on M-605 tells us that a trade assistant is to make three deliveries by string (of animals) consignment. The durable nature of the copper suggests that this may have been a contract. It is consistent with the possibility of a long journey by caravan.
Image Credit:
Indus Script Sign Number 405: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.