Reflective tape. They also make that reflective tape in small strips as to where you can make a design or just outline your helmet. Go to a sign and safety logo store and check out what they have. My friend just put a bunch of Firefighter stuff on his bike,, stands out when the light hits it at night like a mini-firetruck.
__________________ Biketoberfest 2006 flashback courtesy of Intimid8er: "Like you knew damn well you shouldn't eat something like that, but all be damned to hell, you were gonna eat it!" 
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