Look at the lower right corner of the BOX that people post in. There is a yellow, blue, green and red icon. You won't see them in your own posts but they are there in everyone else's posts.
The purpose of them is to let the ember know that you LIKE, (Yellow thumbs up icon) THANKS ( Blue icon) AGREE (Green check mark) or DISAGREE
(Red X).
The members that have a LOT of "reactions" are often the ones that post a lot of content that the members approve of. The real high reaction scores often come from members that post a lot of pictures and memes.
I don't know if the RED X reactions are counted in the "Reaction Score".