So this Fathers 4 Justice bloke scaled a wall and sat on a Buckingham Palace ledge dressed as Batman for five hours. Security breach, hand-wringing, etc.
Various rentaquotes are subsequently wheeled in and out of media interviews. Something Must Be Done, won’t anyone think of the children, etc.
And then the comment I’ve been waiting for. J. Random Expert declares that the police could tell that he wasn’t a terrorist because he was dressed as Batman.
The obvious follow-up question — so what does a terrorist wear, then? — is sadly not asked. I note without comment that the self-proclaimed “comedy terrorist” who invaded Prince William’s birthday party at Windsor last year was dressed as, er, Osama bin Laden.
Avaragado's blog 
Easy answer
Terrorists are easy to spot. When given government mandated ids, they will automatically turn around and say “thats a fair cop gov”.
Dodgy
That photo is way more dodgy when you look at it as they (presumably) filmed it: