I'm not quite sure what you mean by "motto," but if you mean "mission statement," which Merriam Webster defines as a "motto," then I believe it's the first part of their About Us page.
It says:
"We live for innovation. We encourage imagination. We challenge the ordinary. We believe in pushing the envelope. We love the adventure. We respect all of those that respect the art.
theory11 is a group of 11 individuals united in an unparalleled, strategic alliance under one goal, one mission, and one objective: to advance the art of magic."