I agree with "Liking", thus I use it for acknowledging replies, and / or agreeing with what was said.
Many people have asked for dislikes (such as YouTube has) but the owners of Discourse do not believe in letting people anonymously "dislike" posts, saying it is not actual discourse. Ie, if you disagree strongly enough then (they say) you should state why. I disagree because without balance a "like" is meaningless.
I wish we (Discourse users) all had full rights (and means) to like what we will, dislike (thumbs down) what we must, acknowledge (hat tip) what is deserving, and agree (nod) with what we'd wish we ourselves said. (I wouldn't mind a modifier popup choice that allows us to give the "response ticket" a reason like "tone", "spam", "offtopic", "substance", etc.)