This is a pictograph of a tally stick. The three horizontal notches on the stick mean that the unit count was precisely three.
Illustrative Text Reference:
Bala-kot: Seal: Blk-1 A (You should note that the inscription would have a mirrored orientation in the sealing.): Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 391: Collections in Pakistan: Suomalainen Tiedeakatemia.
Image Credit:
Three Notches: Lynn Fawcett, 2017.