This is an ideograph that combines a webbed foot with the contour of an area. In other words, it refers to the shape or form of a water bird. It was used as a classifier (counter or measure word)
Cormorants are renowned divers, so perhaps a modern translation might be the word diver.
Illustrative Text Reference:
Mohenjo-daro: Tablet: M-1429 A: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 386: New material, untraced objects, and
collections outside India and Pakistan: Suomalainen Tiedeakatemia.
This symbol takes up the full height of the character area.