The Indus Dictionary Project
In this composite Indus sign, there is a square within a square. The larger square is an area of land. The smaller square is a boundary marker for that land.
The land has some water, which is depicted as flowing from top to bottom in the image. The three lines in the water symbol indicate that there is a high volume of water in the channel. Therefore, this water symbol is an ideograph for an irrigation canal.
The composition can be read as 'the boundary marker for the irrigated land'.
Kalibangan: Copper Axe: K-122 A: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 326: Collections in India: Suomalainen Tiedeakatemia.
This is Mahadevan's sign number 236 which I have redrawn to better reflect the original engraving.
There is only one extant example of this Indus sign.
Irrigated Land: Lynn Fawcett, 2017.