You can't trademark an "idea", but you can trademark a "brand".
A quick Google search for trademark will take you right to the US Trademark Office website with more information (if you are in the US). There's also a trademark search link in the left hand navigation menu of this website under "Resources"
A forum community dedicated to T-shirt merchants, professionals and enthusiasts. Come join the discussion about graphics, commerce, dyes, prints, collections, guides, displays, styles, scales, equipment, accessories, reviews, classifieds, and more!