It's not illegal to dress as a clown and you don't need to get special permission. But it's statewide that dressing as a clown to cause fear or intentionally alarm/startle people is illegal. It comes down to how you act while dressed as a clown and some behavior that's okay for people dressed normally is not okay when dressed as a clown. Ridiculously ambiguous law, gives the police broad powers to harass anyone dressed as a clown and claim that their behavior was threatening.
And I for one say that the law doesn't go far enough. All citizens should be specially deputized to deal with the clown epidemic. We should all be issued stun guns and batons and be authorized to remove clowns from public places by any means necessary. I'd stop short of giving out awards for turning in clown pelts though, that sounds like overkill at this point. Maybe make it into a game, post running tallies in the paper like the high school football scores. "Fred Smith of New Haven bagged 11 clowns this week, narrowly edging out John Jackson of Hartford who got 9 clowns and a mime. Bob Roberts of Stamford had claimed 14 victories, but he was disqualified as 5 of his "clowns" turned out to be exceptionally pale crossing guards."