The sign shown above is a 20' x 30' high-definition LED billboard on Hwy 99. It offers 1,536 "spots" per day, where a "spot" is a seven second ad showing.

Smart Signs use a SmarTrak RMS "Full Spectrum" electronic tracking module developed by Mobile Trak, Inc.

When a SmarTrak RMS sensor is installed on a Smart Sign Media digital billboard it monitors the passive "local oscillator" signals emitted by the FM radios of passing automobiles. Those signals reflect the frequencies to which the radios are tuned. The Full Spectrum system compiles that statistical data and calculates the number of passing motorists, sorted by the stations to which their radios are tuned. Those calculations are commingled with SmarTrak's Media Audit database that contains detailed consumer demographic and purchasing pattern information segmented by radio station format) in order to provide a complete "picture" of the passing motorists.

For example, Smart Signs could inform passing motorists about special offers to shoppers as they approach stores or malls. A Smart Sign could entice consumers to respond via text message to a question posed by the sign. Information can even be pulled off the Internet and displayed.

Smart Signs are not as intrusive as some systems which actually query cell phones passing by to obtain personal data; see these stories for examples:

- Sprint RFID Loyalty Card Triggers Minority Report-Style Ads
- French Billboards Call Your Cellphone
- BluScreen Minority Report Ads

Electronic billboards in general remind me of a story by science fiction writer J.G. Ballard. His short story The Subliminal Man predicted the use of enormous electronic signs to convince you to BUY NOW:

Franklin paused, looking up at the huge metal sign mounted in an enclosure at the edge of the car park. Unlike the other signs and billboards that proliferated everywhere, no attempt had been made to decorate it, or disguise the gaunt bare rectangle of riveted steel mesh. Power lines wound down its sides, and the concrete surface of the car park was crossed by a long scar where a cable had been sunk... A dim but powerful humming emanated from the transformers below the sign, fading as he retraced his steps to the supermarket...
"You've been rambling about these signs for weeks now. Tell me, have you actually seen one signaling?"
Hathaway tore a handful of leaves from the hedge, exasperated by this irrelevancy. "Of course I haven't, that's the whole point, Doctor..."
(Read more about subliminal billboards)