I was surprised when I could not find any persistence of vision projects on the web using a basic stamp.
Initially I used a piezo speaker to beep each time the pov pattern was complete. This allows you to synchronize your waving motion with the message display. The final pov implementation uses a Memsic accelerometer to figure out when to reverse flash order.
Step 1: Build the circuit
I used the integrated bar LED DIP, but a row of single LEDs should work just fine.