This ideograph might be thought of as a pictograph of the upper torso and arms. The space between the two arms is the distance from side to side, which gives us the width or span of something. Hence, Mahadevan's sign number 225 is the noun span.
Illustrative Text References:
Dholavira: Seal: SI. Number: 15: Acc. Number: 4341 (NB. The photograph is of the seal. Therefore, the inscription would be the mirrored image of that seen in the photograph.): R.S. Bisht, 2015: 8.2.3 Details of Individual Seals: Excavations at Dholavira (1989-90 to 2004-2005), p. 262: https://www.scribd.com/document/262316120/Excavations-at-Dholavifra-1989-2005-RS-Bisht-2015: Accessed: 27 November, 2018.
Harappa: Stone Object: H-1506 A: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 202: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-623 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 4: Collections in Pakistan: Suomalainen Tiedeakatemia.
Comment:
In inscrption H-1506, Mahadevan's sign number 225 is only half the height of the character area. This suggests that it refers to a small span or dimension.
Image Credit:
Indus Script Sign Number 225: Sign List of the Indus Script: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.