1) There is not.
2) No. tracespray can give false results when multiple sprays are sprayed on top of eachother. If for example I spray over an obscene spray, but my spray renders with a lower z-index, then in game mine will be covered by the spray I attempted to spray over. However tracespray will return my name anyway. The only surefire way to solve a dispute of "that isn't my spray" is to request that they spray in a pre-defined spot. Per the answer to #1, they either spray a different spray and go on their merry, or they refuse to comply and you can assume their guilt.