[mttjj]

Those are comments that have been predominately downvoted.

From the FAQ: https://news.ycombinator.com/newsfaq.html

> Why don't I see down arrows?

> There are no down arrows on stories. They appear on comments after users reach a certain karma threshold, but never on direct replies.

[OGWhales]

Thank you! I wasn't aware there were even downvotes, so I didn't think of that as a possibility.