According to a post by Maynard on the Asylum messageboard:

Please don’t bring previously purchased bottles to this signing.
It’s illegal to bring bottles in that were not purchased at Whole Foods.
You will be required to purchase a bottle there for signing.
and PLEASE don’t bring band related items.
This event is about the birth of Arizona Stronghold Vineyards.
Not about rock dudes.

Thanks to Khadgar346 for the tip.