This is a pictograph of a mat with each short edge split into three units. It therefore denotes a floor or pitch area with a width of three standard mats. In addition, the centre of the mat is marked with two counting rods. The rods have been set at an angle, which indicates that the length of the area had not been measured, but was approximately two mats.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-228 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 57: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 2502: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.