This is a deliberate reversal of Mahadevan's sign number 1018. The guard has his back turned, which would make him ineffectual. In context, the translations include relaxed, off-duty and
off-guard in the sense of inattentive, and may be associated with drunkeness.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-72 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 31: Collections in India: Suomalainen Tiedeakatemia.
Indus Script Sign Number 1018 (mirrored): List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.