Stars are fine, and Flying Hellfish of the mushroom cloud is an interesting one. However, I would personally refrain from using any types of ticks for the badge. How about a white hat or something?
I personally don't like the "cop" theme (I don't want to be seen as a cop hehe). I also think we can come up with something more unique than check marks or badges or stars (no offense intended).
Fedora, white hat, top hat is pretty good. But I think something that other forums don't have would be cooler!
Maybe the mushroom cloud could be black for 300, half red for 1k and full red for 5k!