I think you're a clansmen if you think of yourself as one and the chief accepts you as one (or positively doesn't reject you). I have a lot of Scottish blood flowing through me. I could belong to many clan societies, but I don't. I belong to the Clan Cumming Society USA for personal/genealogical reasons. I also have a great interest in my Drummond ancestors (weavers from near Melrose). If I bore a Scottish surname, I'd most likely belong to that clan society; however, I don't.