Pinwheels are a GREAT idea! Our local team that trains for the Leukemia/Lymphoma society bike rides decorates their helmets on ride day with pipe cleaners fashioned into tornadoes. They attach flying cows, houses, etc and it looks hilarious. I'll try to find a picture. Of course, nobody over there might know what a tornado is so it may not hold the same humor. Is there something regionally funny/silly that would make people laugh? Don't know- that's not a good idea, but it's the only one my brain comes up with at the moment.

I like the wig idea, too. You ladies are quite creative. I put a santa hat on my helmet near Christmas- that would not be good in the summer.