TextWave is an android app that lets you use your phone to display large text by scrolling a message as you wave it back and forth. Like a persistence of vision display but with the full resolution of your phone.
Go download it on the Play Store.
You can also just clone this project and import it right into android studio. It should be set up to just build at the push of a button. Warning it won't really do much in the emulator because you can't really wave it around.