The term "certified" has been corrupted to some degree by Moissanite sellers who claim that the Moissanite they sell is "certified" because it comes with the C&C warranty card (which C&C also calls a "Certificate of Authenticity"). Because it comes with this warranty card / certificate, the Moissanite is sold as being "certified".
However in the diamond world, a certified diamond is a diamond that has been analyzed and graded by a gem laboratory based on its "4 C" attributes of cut, color, clarity and carat weight. This is much more than a generic Moissanite warranty card.
At MoissaniteCo.com we do sell certified Moissanites that have been analyzed and graded by a 3rd party gemological laboratory (Imagem). Here is an example of the lab certification.