What are Reaction score/Trophy points?

It's a slightly silly award system. You get "trophies" for different accomplishments on the forum, like uploading an avatar, having reached a certain amount of posts, getting your first 'like' etc.
The reaction score is just keeping track of the amount of likes/smileys under your post.
As Artyczar's legal representative I would like to state for the record that no actual trips, tickets, or vouchers for travel to Hawaii, Guam, Chiswick, Baltimore, Vladivostok, or the Lesser (or Greater) Antilles will be awarded, bestowed, or inferred from the Creative Spark website, its subsidiaries, or its owners. Thank you.

(But I did hear that Wet Canvas is giving away a single bleacher seat ticket to a minor league baseball game in Kansas City, Missouri, so you might want to give that a shot. I mean, they may give it away or they may not. They have to have some meetings with corporate to decide. And that decision will not be specific or even make any sense. But hang around forever anyway to see what happens.)