The Sindhu Saraswati Civilization was a Sanatani one and not “Hindu”. If you are asking whether it is as Hindu as a 21st century Indian, then it is a no. However, if you are asking whether they practiced a religion that closely resembles traditional Sanatani culture, then it is a yes.
We have found multiple evidences of religious continuity throughout the civilization. The existence of Shiva in Sindhu Saraswati Seals as Pashupatinath, the Lubdaka Seals, the mention of Rudra (Shiva) and Vishnu in Vedas and in later Puranas prove this religious continuity.
Among religious practices, the usage of idols, and ritualistic bathing also act as evidence of religious continuity.
Finally the site of Bhirdana which was inhabited from 8th millennium BCE to the first millennium BCE also acts as a strong evidence of continuity against the argument of an urbanization gap mentioned by some scholars.
Please note that the word Hindu itself is a Farsi (Persian) corruption of the word Sindhu and was coined around early 19th century to name the native religious practices of most of people residing in the British Raj (not India).
The Continuous Religious Tradition of Shaivism
Shaivism has existed in one form or another since the early days of Sindhu Saraswati Civilization.
The first account of Shaiva worship is found in the Pashupatinath seal which was discovered in Mohanjodaro. The seal was dated to 2350 BCE to 2000 BCE.
We find another point of Shiva Worship in the Lubdaka Seal. This seal was discovered at Harappa and shows the Lubdaka Story which is a narration on how Mahashivaratri originated.
Possible Idol Worship
Plenty of Idols have been found in several Sindhu Saraswati sites like Mohanjodaro, Harappa, that represent some kind of representational revering or worship.
Among them the bust of the Priest-King-Headman is the most famous. Scholars have long debated whether the statue belongs to a real person (king/priest/headman) or is the statue of a deity.
There is another sculpture which shows a monkey figurine. It could be just a toy or a representation of Hanuman.
The idol is seated in the rear, second from the right.
The largest idol which is also the rightmost one.
The discovery of Swastik Button seal in Mohanjodaro is another evidence of religious and cultural continuity.
Swastik is still relevant in modern Sanatani practices and is a symbol of prosperity.
Ritualistic Bathing
The great bath discovered at Harappa shows ritualistic bathing in the middle of a city, somewhat similar to what we see near ancient Shiv temples like Trayambakeshwar Temple where a bathing tank exists at Kushvrat Tirth near the temple.
Even todays, Sanatanis practice a ritualistic bath everyday before beginning their daily routine.
