After the attempt, the company will display the coupon on the side of the nearby W Hotel all day long and anyone that snaps a photo of it (you can also share it with others) can redeem it at any Jack in the Box nationwide for a buy one, get one free Buttery Jack by showing it from their cellphone.
If you happen to live in the Los Angeles area, you can catch the event live starting at 9:30 AM at the Jack in the Box at 6407 Sunset Blvd, Los Angeles, where Jack himself will redeem the coupon.
Afterwards at 11 AM, Jack in the Box will be throwing a party at the parking lot by the W Hotel at 1634 Argyle Ave., where you might meet Jack and there will be a DJ, a selfie station, free Buttery Jack burgers, and the giant coupon on display (I'm not sure how long the party will go on for).
Update 3/26 - Here's a photo of the coupon provided by the company. You can use it through April 1, 2015: