No, it is not a new rock band -although it would be a cool name,- it is the unofficial solicitation for December's Birds of Prey # 4. Batgirl will make a guest appearance in the book written by Duane Swierczynski. DC promises that the issue will have "a shocking revelation [that] is going to upset the status quo all over again".
Birds of Prey #4
Art by David Finch and Richard Friend
December is still far away, but in the meantime we can speculate. We are assuming this is Barbara Gordon, but why is she looking so much like Stephanie Brown? Is this a coloring error in the character's armor or her hair? Is the miscoloring intentional? On top of that, Gail Simone -writer supreme- claims having no knowledge of this guest apparance, which only helps to fan the flames of controversy. If this turns out to be the case, then DC owes Ms. Simone a big apology; if it's just some kind of marketing stunt, then it worked... I am interested, because I was not going to get BoP, but now I am, only because of this image.
The way I see it, whoever that is in the teaser, everyone wins. If it's Barbara, then old Birds of Prey fans will be happy to see her and Dinah reunited. Barbara will have more exposure and fans will be happy to know that their favorite character is being used to boost another book's sales -not the other way around. Now, if it turns out this is Stephanie Brown, then her fans can be happy that she has not been removed from the new continuity and has found a home in the BoP book. It is not the end of the world if there is more than one Batgirl; ask Batman Inc.