This composite character comprises the adjective summer with a pictograph of 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 2699 is the noun summer help.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-409 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 98: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 2699: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.