The MS-ISAC, a group established to "improve the overall cyber security posture of state, local, tribal and territorial governments", isn't even waiting for people to hack traffic signs to blame it on video games. It's getting out ahead of the trend.
A recent report issued by the body, about a notorious "Saudi Arabian actor" who has been defacing various websites and electronic traffic signs in the US, says that he recently tweeted an image from Watch Dogs. And that's enough for them to man the ramparts.
CIS believes it is likely that a small percentage of Watch Dog players will experiment with compromising computers and electronic systems outside of game play, and that this activity will likely affect SSLT [state, local, tribal and territorial] government systems and Department of Transportation (DOT) systems in particular."
I love how not even an official report can bring itself to call it "Watch_Dogs".
They Hack Because They Can [Krebson Security]