This symbol is a combination of the contour of an area and a pictograph of flat stones. An area of flat stones gives us the noun foundations or footings.
Illustrative Text Reference:
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.
There is only one extant example of this symbol in the Indus texts.