Nikki shares her wax seal stamp tutorial with us here. She makes a simple innie “stamp” but you could certainly use any other stamp or sculpt a low relief design to use. If I were to use this with sealing wax I would make sure to use an outie (raised letter) stamp design and some sort of release like Armor All so the wax did not adhere to the clay or get in nooks. The little faux wax seals are adorable enough you wouldn’t need to use wax though. Just make your own seals.
She provides a link to the faux seals tutorial as well.