Well, anytime anything happens anymore, they are going to take credit for it. I'm waiting for the Al Q press release stating that the earthquake(s) on the east coast were their responsibility, lol.
I just don't think they'd be so blatant as throw up a picture of something they are going to attack, except to try and scare people or make them jump to conclusions (and thereby divert their attention).
The government is in a bad situation right now - anytime anything like this happens, they have to take it seriously, or at least check it out, otherwise if something did happen and they had ignored the warning signs, you could have more Americans dead and a lot of government officials losing their jobs (yes, I've known politicians who cared more about their jobs than the American people). The FBI/CIA/etc. got a "get out of jail free" card with 9/11, if something else happens that could have been prevented, a lot of bureaucrats' heads will roll.