Taco has a contest to win a PlayStation Vita. Just enter the code from the $5 meal box. If the code isn't a winner you can enter 2 other ways by playing some game on the iPhone or Android. A third it to boast about what you do to get your hands on one first.
The second way has you upload a video or picture.
Some ideas is to draw a PLA/Taco Bell logo. Another idea is to post a video overtaking their drive PA system. Or placing a sign at their drive thru speak saying "Sing happy birthday to the drive for a free meal of your choice."
I know both pranks have been done in the past. Post other ideas you have. Your prank will probably win you the newest PlayStation contraption.
MIB