Hello!
As others have mentioned (thanks, @BunnyCat and @Newpetlover), the button previously had a function on the Forum, but over the last few years, we changed how feedback is collected and passed along by the Forum team.
Although we’re not actively using the feature to collect data, you’re welcome to use it as a way of showing support for a post without engaging, but I always recommend commenting on or using the heart emoji to “like” a post/reply for the best Forum experience. 
Jenny