my guess is that people can like () individual posts.

The positive of that is:

a) possibility to like () just one post, or 2, 3… depending of who good the thread is

b) the fine granular way to like () gives the algorithm way better possibilities to whom to show a thread and even better, to first show just one intereting post out of that thread (also people can mores easily quote or retweet individual parts of a thread)

Why are you adding () after "like"? Havent seen that convention before, so I am unaware of the meaning.

There may have been an emoji or Unicode character between the parens that was stripped by HN.

That does make quite a lot of sense.

correct, it was a "thumbs up" emoji

I was assuming there's a trademark symbol ™ that had been stripped by HN. But since I've managed to post one, I'm apparently wrong!

Or retweet individual posts. It makes each one a possible pull-quote.

Yep; everything's a soundbite.