Trademark is different from copyright, which is what you mean - claiming the wrong thing might give you problems if you ever try to enforce it. You can add a comment to an OBJ file, but it can easily be removed: as well as, or instead of, that you should put a readme file in the zip with the objects saying what they are, what restrictions you put on them (can they be used for paid work? Can they be redistributed freely (if so you would usually say the readme must be included)?), that they are copyright treeabear (or your real ID) and provide some sort of contact. There is a Copyright forum here - it's towards the bottom of the list.