You have to get past the Joker's cryptic riddles, but here is what it says...
Gather with 300 of your closest friends at this exact spot on April 28th.
You'll need to be in contact with a partner-in-crime who has online access to relay your instructions once you're there. These instructions will give you the TRAIL to follow, but be sure to look both ways when crossing the street; we wouldn't want you to make an unscheduled visit to the ER now, would we?
Put on a smile and plan to spend about an hour or so bonding with your fellow clowns.
Check back here often for updates or changes.
Did you see the TRAIL-ER in the message? Hmmmm.