These morons couldn't tell Arabic from Armenian. And who is going to crawl around under aircraft spray painting Allahu Akbar?
The real question is: Is this a case of an inside job or someone circumventing access and perimenter controls? If someone is able get near enough to a plane to graffiti it, they are also able to get near enough to sabotage it or plant a bomb on it. As we know from the GAO report, perimeter and access control is a weak area for TSA. TSA agents have been known to escort criminals around security check points. And the TSA airport worker credential program is a mess as discussed earlier on TUG.
Whether it's an inside job or an unauthorized person getting access, it only shows another hole in airport security, while passengers are being abused.