In Mahdevan's sign number 308, the adjective armed is surrounded by four points of darkness, one in each cardinal direction. Each point of darkness signifies that something is false. Hence, the
image is false for each direction, in other words, it is never true. Thus, this is an ideograph for never armed.
Illustrative Text Reference:
Kalibangan: Seal: K-15 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 301: Collections in India: Suomalainen Tiedeakatemia.
There is only one extant example of this Indus sign.
Indus Script Sign Number 308: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.