An earlier use of zero (as defined in the article) for which one can assign a definite date was in 357 AD. The gotcha is that it's not the circle we're so familiar with. This is the first Mayan (Olmec) long-count recorded containing a zero, although long-counts showing a clear positional number system were recorded in the first century BC.

http://books.google.ca/books?id=TzrNgAsJY1MC&lpg=PP1&...

While the use of zero in India may have been influenced by earlier cultures (e.g. Babylon), it's pretty unlikely there was any direct contact that could have spread the use of zero to mesoamerica. Thus, positional number systems with a zero place-holder have been invented independenly at least twice in human history!