A theme normally posts to wp-comments-post.php when someone leaves a comment. When successful, it does a redirect to the page again but tacks on "#comment-" into the URL. What I was wanting to do was leave a message, "Your comment awaits moderation, which takes about 24 hours." Sure, I can intercept location.href and see if it contains "#comment-" in it, and show the moderation message then. But there are other ways one can click on a page and "#comment-" gets shown, which makes this a visual quirk, not the way I intended it.
What's an easy way to make a WordPress theme detect that a comment was just posted and redirected back to the page?