Simon Property Group has installed billboards that use shoppers' car radios to tailor ads. Wal-Mart Stores says Wal-Mart TV boosts sales better than network or cable TV. And plasma-screen displays are becoming de rigeuer at clothing stores across the mall.

Digital P-O-P is booming, thanks to shrinking costs, growing bandwidths and jaded shoppers.

“Everyone has a plasma screen in their window,” says Nikki Baird, senior analyst with Forrester Research. What started with tech retailers like Best Buy — whose products are TV and computer screens — has spread to apparel, housewares and groceries.

But retailers have yet to maximize digital signage or in-store TV, Baird says. “It's early on the learning curve to find the most effective message for in-store TV; about all retailers know so far is that a regular 30-second spot isn't very effective.”

Marketers also need to devise a new measuring stick — one that is tied to sales, since it's at point of sale — to replace traditional TV CPMs for pricing and ROI. And marketers need to step up content to keep it fresh and targeted, Baird adds. “These dynamic media are voraciously hungry for content. Brands could apply what they're doing with online retailers to in-store digital P-O-P,” Baird says.

Simon has signed two advertisers, DASS Salon & Spa and Brand Atlanta, for digital signage at its Atlanta mall. (Non-profit Amber Alert is using similar signs at Simon's Westminster, CA mall.) The signs pick up FM radio signals in passing cars and tailor ad messages to the demographics of the radio station that's playing. The signs also give passers-by text codes to request more information via cell phone. Simon calls it “outdoor narrowcasting,” via digital wall signs, entrance marquees and freestanding signs seen by 19 million-plus shoppers each month. Content touts mall-specific brands, retailers and events. Smart Sign Media and LED Partners VI manage the signs; management consultancy Accenture oversees the venture for Indianapolis-based Simon.

Wal-Mart TV triples purchase intent, compared to network or cable TV ads, according to Premier Retail Networks, which runs Wal-Mart TV. A survey of 5,500 Wal-Mart shoppers found that 15% of shoppers who saw a brand on Wal-Mart TV plan to buy it “today,” compared to 4% who only saw a brand advertised at home. Fully 85% plan to buy a brand advertised in-store “in the future” (compared to 62%). Media research firm TNS conducted the survey for San Francisco-based PRN.