I agree with MTS wholeheartedly. I only enter our small regional show and though it's not required, I always mention in my exhibit tag that my quilt is an original design.
Here on the QB, while I don't think it's something that should be required, it is courteous and proper to give credit to the designer of the quilt when posting it. Generally if you don't do that, and your quilt is admired, someone will ask.