I'm not by any means a licensing expert, however, I do know that organizations' coats of arms, letters, logos, and other such marks are nearly always trademarked and protected. Members may claim fair use of them to a point, but if a profit is being made by any party they should become a greek licensed vendor (here:
http://greeklicensing.com/).
I'm not sure if it would be enough for Spoonflower to become a greek licensed vendor, or if each individual seller would also have to conform to those guidelines.