One way is when we enter India at borders, they check out exit dates in system. Usually people who are still indians would have US's some kind of visa. US Citiz

One way is when we enter India at borders, they check out exit dates in system. Usually people who are still indians would have US's some kind of visa. US Citizens will not be able to show any US visa. There are heavy fines for not self surrendering the indian passport after US Citizenship within 6 months.