When two silkworms spin their cocoons close together, the cocoons become entangled. The resulting thread is uneven. In modern sericulture the uneven thread is used to produce slub silk. Hence, this pictograph is the noun slub silk.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-143 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 45: Collections in India: Suomalainen Tiedeakatemia.
Comments:
There is only one extant example of this Indus sign.
Note how Mahadevan's sign number 2002 accurately depicts the primary filaments being extruded from two glands on each silkworm.
Image Credit:
Indus Script Sign Number 2002: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.