The shape depicted in Mahadevan's sign number 261 has a large and a small size in Indus script. Each size represents a different pictograph, and takes a different meaning.
In its smaller form, this pictograph is an outline of the lips when the mouth makes the long O sound of the vowel O. Hence, the symbol is an ideograph for the nouns voice or noise. Other translations include the verb to shout. The sign shares a common root with the Chinese character kǒu 口. Although the shape of the symbol has changed in modern Chinese, the word kǒu has retained the long O sound.
In its larger form, the pictograph is a diagram of a perimeter wall portrayed in accordance with the Indus convention, whereby the north-west point is centred at the top of the character area. The larger sign shares a common root with the Chinese character wéi 囗.
Illustrative Text References:
Shout: Mohenjo-daro: Seal: M-306 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 76: Collections in India: Suomalainen Tiedeakatemia.
Edge: Harappa: Pottery Graffiti: H-2549 A: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 351: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Comments:
In inscription H-2549, you should note how the author has deliberately used a larger scale for this symbol than for the other characters. He wanted there to be no doubt that the inscription refers to the edge or perimeter of the footings.
Conversely, the engraver of inscription M-306 used a smaller scale for this symbol than for the other characters.
Image Credit:
Indus Script Sign Number 261: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.