Sun is very distinct through the eclipse. You go from bright sunlight to twilight in a matter of 10 seconds. And everybody around you will start screaming like the home team just made a touchdown at the Super Bowl. It will be unmistakable when it's safe. Plus, if you're looking through the eclipse glasses, the crescent sun will get thinner and thinner and thinner, and then it will vanish. Then it's totality, and it's safe to look.