Just like on YouTube. You can either click on Like or Dislike and it will record your choice and be visible to everyone. You should be able to change your voting at any time. The comments could additionally show a small icon that showed if the person liked or disliked the current thread.

This might be a good idea on the suggestions forum, except the problem of people voting on multiple accounts. While I am sure the devs could do some stuff to mitigate it, completely stopping someone who is TRULY determined to abuse such a system would be WAY more work then it'd be worth. If it would even be possible at all. It's not that hard to have several R/L friends vote for your suggestions.

As for all the other forums, I can't see any benefit to it, or at least nowhere near enough benefit to justify the effort involved in adding such a system.

Well I am pretty sure the +1 -1 is already abused in the same manner. But this is also a -1 from me, for the simple fact that you should add an explanation to your opinion rather than simply clicking a like/dislike button.

People already say "-1" without explaining anything so that wouldn't change. And the comments would still be the same but they might show an icon next to a comment that indicates if the author of said comment agrees or disagrees with te current suggestion.

Would just cause more reasons to argue:

"Soso's post didn't get any likes but it still got implemented you fascists!"
"My post got 500 million likes but nothing you fascists!"
"Soso's post got 500 million likes this has to be unsupported plugins you fascists!"

etc etc

Although people +1 and -1 things without discussion, how would this help with that also? I do not think people +1'ing a suggestion has ever led to it being done without further discussion on the topic anyway, or unless the developers see merit/balance/already part of the vision in the suggested idea.

so -1

-1