The term POV is for Persistance of Vision, I don’t want to bore you with definitions or explications, just look at the next picture:
The project is very simple, first of all because this type of display is the easiest to build, and because the author made it only for three letters, this way everybody can understand the basic principles and extend the functionalities.
The source code should be optimized and added some position sensing to synchronize the image. The schematic isn’t available but form the source code is easy to reverse engineer, since each led is driven from one micro controller pin.
If you add an accelerometer then you can stabilize the image even when rotating by hand, off course the overall weight must be reduced. With some wireless link you could even refresh the image dynamically.