This is a symbol for a door leaf combined with the ideograph for an equivalent measure. The composite symbol then becomes an ideograph for a standard sized door.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-360 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 90: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Standard Sized Door: Lynn Fawcett, 2018.