The Indus Dictionary Project
This is a pictograph of a stylised hand. The hand is outstretched. Hence, this symbol is an ideograph for the negative form of the verb to do: do not.
Chanhujo-daro: Seal: C-23 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 333: Collections in India: Suomalainen Tiedeakatemia.
Mohenjo-daro: Seal: M-1707 a: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 23: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
This is Mahadevan's sign number 1139, which I have redrawn to better reflect the original.
In the context of inscription C-23, the verb takes the past tense: did not.
Do Not: Lynn Fawcett, 2019.