Could you please email us (hn@ycombinator.com) a screenshot of what you see here?

https://news.ycombinator.com/upvoted?id=DSingularity

dang is very active and often sees these @'s, but there isn't actually any notification-like behavior on HN (or at least there wasn't a year ago). I've emailed hn@ycombinator to let them know there might be some bug here.