It looks like Google is testing a like button, thumbs up button, on some Google Posts within search and maps. Brodie Clark shared a screen shot of this in action on Twitter. You can see the thumbs up icon at the bottom right corner of the post.

I personally cannot replicate this, so it might be a limited test or maybe it is a feature just now rolling out.
Brodie was able to like his own Google Post, which I guess is okay since you can only like something once with a single Google account.
Forum discussion at Twitter.

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