One of my Christmas presents that I received was a Pro-Tec helmet. Of course, I wanted to add reflective tape, but I didn't want to end up looking like a safety dork or like a Coast Guard Wannabe. So, I picked up some black reflective engineer's tape. In normal light, the tape looks like black electrical tpe. But, when you shine a light on it, it reflects back a bright white.
Definitely a safety dork. Note that this pic was taken with a flash, with no tape on the helmet.
Safety Dork in profile.
Black Engineer's tape applied, photo taken without a flash:
Same helmet, same black tape, only this time taken with a flash:
Note that you can get Engineer's tape in a number of different colors, so you add reflective safety tape to your helmet without fear of looking like a safety dork.