Bernstein Research’s Todd Juenger says today that it’s a possibility after CBS unloads its billboard business. It’s widely believed that the company will use the cash it raises for what the analyst calls “a massive buyback” — possibly as much as $8B, or more than a quarter of CBS’ market value. Ordinarily that would be greeted by cheers on Wall Street. Nearly every Big Media company has a huge stock repurchase plan, part of CEOs’ efforts to appease investors who fear that the industry’s glory days will fade in the Internet era. Moguls may not understand digital media, but they know simple math: Earnings per share rise when a company reduces the number of shares. But if CBS takes the strategy to an extreme with a ginormous repurchase, it may be surprised by the Street’s muted response, Juenger warns. Recalling the infamous scene in Happy Days when Fonzie water-skied over a shark — signalling the audience that the show had run out of ideas — he says the company could create “a seminal ‘jump the shark’ moment, triggering media investors to re-evaluate what all these buybacks — at the expense of doing anything else — are really doing for them in the long run.” In CBS’ case, the company would be “still heavily advertising dependent and heavily U.S.-centric.” That’s a bad place to be: “Over the long-term, we believe ~2% is the best anyone should assume broadcast TV advertising can grow,” Juenger says. He’d rather see CBS use the cash to buy assets that make it less dependent on U.S. TV ads. The recent acquisition of half of TV Guide Network is “one small step in such a direction.”