If America's bosses are leading by example this summer, investors might want to sell shares. According to analysis by Form 4 Oracle, named for the stock transaction reports that executives, board members and major stakeholders must file with regulators, the ratio of companies with net insider buying to those with net insider selling is the most bearish it has been in two years.

Insider selling generally isn't worrisome. Bosses have plenty of reasons to periodically unload the stock they're given as pay. Sometimes they diversify their holdings, or free up money to buy a house, or, I don t know, fill an in-ground swimming pool with cognac and tears of the working class. Still, the four-week buy/sell ratio, which was more than 60% at the start of 2009, recently fell to 33%. A drop like that suggests insiders are either strapped or skittish, or both.

A few are still buying, of course, and whereas insiders have many reasons to sell, they have only one good reason to buy. Well, maybe two. The first is that a contract they signed when they joined the board mandates a minimum level of stock ownership. The second and more common reason is that they think the stock is going up. As insiders, they re in a good position to predict that sort of thing.

Big stock purchases bode well, but there s more than size to pay attention to. A string of buys by multiple insiders bespeaks agreement. Executives with chief-this-or-that in their title tend to fare better on stock trades than directors and major stockholders, long-term studies show. Naturally, purchases made by insiders of any type who ve profited nicely from past trades are worth noting. Below are three companies with recent buys of each of these types.

High-Level Buy: Mentor Graphics

Mentor Graphics (MENT) stock has lost half its value in a year. In late June, the company s president bought 20,000 shares at $5 and change. Mentor makes electronic design automation software, and has suffered a drop in demand along with chip makers over the past year. Two years ago the company earned a dollar per share. If it can make half that next year -- early forecasts call for earnings of 52 cents a share -- then the stock trades at a reasonable 13 times earnings. The company is only modestly indebted.

Multiple Buys: Orexigen Therapeutics

Orexigen Therapeutics (OREX) makes no money. I repeat: no money. So why have nine different insiders loaded up on stock this month? The company is a drug developer focused at the moment on a single pill called Contrave. It s a weight-loss drug made by combining the antidepressant Wellbutrin with an addiction-suppressing drug called naltrexone. Phase 3 trials of the pill -- those are the ones that typically come just before a request for approval -- wrapped up earlier this summer. Subjects lost heaps more weight with Contrave than with a placebo, and reported few side effects that would give regulators pause, according to Canaccord Adams, an investment bank. Canaccord envisions Orexigen booking modest sales in 2011, ramping up to more than $250 million by 2014. That s roughly what the company sells for today, net of its cash.

Sizable Buy: Lions Gate Entertainment

Corporate raider Carl Icahn is loading up on shares of Lions Gate Entertainment (LGF). The small, quirky film studio has grown its sales in recent years on a mix of commercially if not societally successful torture porn from the "Saw" and "Hostel" franchises; self-aggrandizing documentaries from Michael Moore and Bill Maher; and a French nature film with marching penguins that, unforgivably, made me cry. Expect Icahn to badger Lions Gate management in the press about failing to sufficiently unlock stockholder value (that is, boost the stock price). Based on Lions Gate s sales, the stock looks cheap. Profit margins are dismal, though. Management is planning a leaner film slate for next year and to ramp up television production revenues to smooth out swings in its movie fortunes. Investors should probably wait for a sustainable pick-up in profits before joining Icahn as an shareholder.