I was looking at possible badges I could earn on CV. I think there was one where you could earn the badge by voting for a specified number of comments. I have seen numbers to the left of some comments. Do they represent votes? I have no idea what to do to vote for comments if it is possible.
Yes, there is. Hover over the left side of a comment and click in the up arrow to vote (try it in the sample comment I left under the question). Comments can't be downvoted. You will also see a flag beneath the up arrow; that is for flagging comments.
Badges related to commenting are 'Commentator' (bronze) and 'Pundit' (silver). The latter is the one related to voting. One needs to write 10 comments and each of them receive at least 5 upvotes (yes, numbers on the left represent the amount of votes a comment received). I think the intent of the Pundit badge is reward users who write useful comments. Likewise voting on regular posts, a user can't vote for his/her own comments.
There are no badges for upvoting comments.