This is a pictograph of a stack of seven counting rods surrounded by a protective cylinder. Hence, it is an ideograph for a set of seven things in a protective cylinder.
Illustrative Text Reference:
Mohenjo-daro: Seal silver: M-1199 a: Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and Inscriptions: Volume 2: Page 142: Collections in Pakistan: Suomalainen Tiedeakatemia.
Comments:
Please note that for inscription M-1199, view a in Parpola is the same as view A. It should be the mirror image.
It is interesting to note how the arrangement of the counting rods within the cylinder is the same as the first two rows of a stack of ten counting rods. In other words, the symbol reflects the actual usage of counting rods.
Image Credits:
Cylinder of Seven, and Ten Counting Rods: Lynn Fawcett, 2018.