This is my "Light Emitting Diode Persistence of Vision Helmet". I made it for my Gizmology class this semester.
On the end of the black arm is a vertical row of 8 red LEDs that are attached to a chip which controls the rate at which they flash. You can program short text messages into the chip via 3 buttons on it's side. When the LED POV flasher is on I then flip a switch on the helmut to engage the motor which spins the LEDs around my head. When in the dark the flashing LEDs combined with the rotational movement give the illusion of red letters floating around my head in a halo-like fashion.
I can't capture the red letters with a still or video camera so you will have to see it in person.
I will have a step-by-step DIY tutorial posted on The Ominous Moo so you can make one yourself!