On what evidences is Indus Valley Civilisation called 'Pre-Aryan Civilisation'?

The Indus Valley Civilization (c. 3300-1300 BCE) is termed 'Pre-Aryan' primarily because its undeciphered script and material culture predate the arrival of Indo-Aryan speakers in India (c. 1500 BCE). The writing system of the Indus Valley is distinct from later Brahmi scripts and remains undeciphered, suggesting it belonged to a civilization that existed before Aryan migrations. While utensils, copper artifacts, and art are all important archaeological findings, the writing system provides the strongest evidence for its pre-Aryan chronological placement.