This is the pictograph of a double-headed drum combined with two diagonal lines that resemble the Chinese character bā 八. Bā can mean all around or on all sides, which is the interpretation that I think applies here. Hence, this Indus sign is an ideograph for the sound of a reverberating drum.
Illustrative Text Reference:
Allahdino: Seal: Ad-6 A (NB. The inscription would be the mirrored image of that seen in photograph Ad-6 A): Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 388: Collections in Pakistan: Suomalainen Tiedeakatemia.
Comment:
Inscription Ad 6 is interesting because it may refer to a signal drum that was used for timekeeping. In Chinese cities, a drum was sounded at dusk. It is possible that the people of Allahdino had the same custom.
Image Credit:
Drum Sound: Lynn Fawcett, 2017.