"We felt like our users should be rewarded and recognized for their good deeds and contributions to the communities so we designed the medal system. Based on your activity within a club you can earn different levels of medals. Think of the medals as a measure of reputation. The higher the medal, the more respected the user in that club."
is what the Fanpop says :x
my reason for getting a medal is that to show people that i really love that club :)
It's a way of showing that someone's been really active in a club, contributed to it a lot and added a lot of stuff which other people have fanned. It's a bit random though. I've gotten a medal for a club which I've contributed less to than my other clubs, I'm sure.