What is the sign of the person born on August 3rd?

That depends on whether you are talking about the solar calendar or the lunar calendar. If it is a solar calendar, it is a Leo. If it's the lunar calendar, it's uncertain, because you haven't given the year, and there's no way to help you convert it into the solar calendar date to correspond to the constellation. If you are interested in constellations, you can download the life calendar, not only to find the constellations, but also to watch the daily constellations for free.