How to mark an answer "Unhelpful"?

[Sergey Popov]

There is a lot of answers in this community that are totally unhelpful, and written only with hoping to get positive scores.

There is a button "Helpful" but no "Unhelpful" button.

Is there any way to vote negatively for a comment?

[Mark Manders]

No, that is not something that is currently possible. I think that's because the solution that isn't helpful to one's question, could help someone else with a similar, but not the same solution. 

The biggest problem with the ServiceNow community is that they made it into a 'click' contest. I think it is very useful to have a 'helpful' or 'correct answer' possibility, because it will help people in looking for those correct answers and skip through the useless posts. But when it's combined with badges and leaderboards, it is getting a lot of people involved that either repeat the answer some one else already gave (hoping it get's voted for) or even post AI generated answers that are only related to the question because it is about ServiceNow. 

The community should be a place where people come to help each other and not for people to gain a certain status. Share your knowledge, but don't go for clicks would be a great motto. A 'not helpful' button wouldn't add any value, because it can also be used in spite ("if I can get 3 more answers than that other person, I will get above him in the leaderboard, so let's vote down".). 

[Sergey Popov]

Exactly! The contest forces a lot of answers that are completely unrelated to the question.

I'd disagree that "Unhelpful" button wouldn't help. It would help eliminating this kind of answers.

P.S. Your message's last line is very funny)

[Mark Manders]

If the goal is to get rid of the useless answers, the 'unhelpful' button would only help if it was counting down the helpful/correct answers. And with that you will get what my last line was about. 

Making is a 'who has the most clicks' community is just bad for the quality of answers.

If the only upside to giving answers would be helping people, you would get rid of of the useless ones. It's a community, why does it have to be a game? If I help my neighbor putting a new floor in his house, I get a thank you. I don't get a 'helpful neighbor' sign in my yard (thank goodness). 

[Sergey Popov]

Yes, the main issue is a lot of useless answers made just for getting score points. 
They are not made to help. Maybe it makes sense to disable this challenge. 
However, having both "Plus" and "Minus" options is a common practice in many communities and social networks.