When you upvote a comment, if you have authored any parent comment in the the thread, your nick should be listed in the comment metadata ("Upvoted by commenters: tqbf, RiderOfGiraffes").
Upvotes/downvotes send conversational signals that incite responses, whether those responses have intrinsic value or not. So do critiques. Seeing the name of someone who just critiqued your comment in a list of your upvoters might neutralize some pointless flame wars.
To an extent, we already have this feature informally, because "I upvoted you, but..." has become an idiom on HN. I think it'd work better if it was automatic though, and it might incentivize "feel-good" upvotes.