There's over three thousand articles on this website, so from time to time I find myself unsure if I've upvoted an article - especially since I've been a member for much less time than I've been browsing the site without an account.
The only way to tell if I've upvoted an article is to click the upvote button. If the upvote goes through, the realization sets in that I never upvoted an article that I was sure that I upvoted prior. If the window comes up saying that I've already upvoted the article, well then I just feel silly.
It's a somewhat clunky cycle. Just having a green dot or something next to the rating module to tell me I've upvoted would just feel smoother.