Yeah, all my research has been saying that Persephone either has no symbol or, as the site you found shows, it has TWO (Proserpina being the Roman name for Persephone), but neither matches the character in question. But I know I've seen that symbol before... maybe in some of my Wicca book or something (in addition to a paper I saw once before, which is probably buried among my things back in CA). Does it look at all familiar to you?