A friend of mine got busted playing a prank on another mates network. A concerned neighbour thought he was 'spying', phoned the police and gave them his licence plate number after seeing him waving an antenna outside the car. Fortunately the cops didn't care at the time (this was a couple of years ago).
I even got pulled over myself testing my own community network over three years ago. The female cop couldn't keep a straight face when she saw all the gadgets set up in the car including a full desktop PC (don't ask) and waved us on with a laugh
You can get magetic mount antennas for cars now (I think Dale sells them), I recently got a 7dBi one and it looks nice and innocent stuck on the roof of the Subie
Awesome stuff for doing surveys/range tests on the community network without some paranoid public trying to report you in for 'hacking'.