The Indus Dictionary Project
This is a pictograph of a cord with a loop facing upwards. In the pictograph, the two ends of the cord overlap. At the point of intersection, we might choose to join them together with a knot. Hence, this Indus sign is an ideograph for the the verb to join or to knot.
Photograph: Plate 7, p. 34 and Drawing: Fig. 3, p. 19: Tejas Garge: Sothi-Siswal Ceramic Assemblage: A Reappraisal: Ancient Asia, Vol. 2, 2010: http://www.ancient-asia-journal.com/articles/10.5334/aa.10203/: Accessed: 22 July, 2016.
I was delighted to find a photograph of this sign on a piece of pottery from Siswal. The object is mushroom shaped. It has five of these signs incised on it. I think that it may well have been used for darning.
Indus Script Sign Number 8211: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.