In this Indus sign, the door leaf symbol is used to illustrate movement on a pivot through 180 degrees.
In the context of the example from Harappa below, the symbol is an ideograph for the noun hinge.
Illustrative Text Reference:
Harappa: Seal: H-477 A (NB. Image A is a mirror of the image that would appear on a sealing): Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 281: Collections in Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Hinge: Lynn Fawcett, 2017.