Not quite Minority report but the Billboards are listening

Billboards That Know You
Not Quite Minority Report...but Listening In - The Mobiltrak DSP Radio Monitoring System is able to detect the faint tuning signal that every car radio emits. Using Mobiltrak technology, advertisers can now identify the listening habits of the drivers who pass their billboards at different times of the day.
Billboards could be listening in on your car radio as you drive past. Using a specially equipped dish manufactured by Mobiltrak, a Phoenix company, advertisers are now able to detect which radio stations drivers are listening to and then alter the messages on their electronic billboards to match the demographic that clusters around those stations. There are only a handful of these responsive signs in operation so far. Source:New York Times Magazine December 14, 2003 by JENNIFER BARRIOS