On Wall Street, "sell" recommendations are exceedingly rare. Perhaps for that reason, they tend to be worth following.

Among companies with the most sell recommendations is Eastman Kodak, which the Wall Street Journal reports this week is edging closer to a bankruptcy filing (see "Kodak Teeters On the Brink").

The large, mid-size and small companies in the S&P Composite 1500 index together have attracted more than 20,000 published analyst opinions on what to do with their shares. Barely 200 of these say to sell. Why? One innocent explanation is that clients of these analysts' firms are more interested in hearing about stocks to buy than ones to sell, because most retail investors don't engage in short-selling, or betting against stocks.

Another, not-as-innocent explanation is that the same firms that issue opinions on shares also court the companies under their coverage for lucrative investment banking business. Over the past decade, regulators have taken steps to reduce conflicts of interest among analysts, and studies show the link between investment banking relationships and "buy" recommendations has weakened. Analysts have also become a bit less optimistic in their recommendations, but a culture of sticking with "buys" and "holds" and avoiding "sells" remains.

Research by Kent Womack, a former Goldman Sachs executive who taught at Dartmouth for 16 years before heading to the University of Toronto in 2010, suggests two things to keep in mind when using analysts recommendations to inform stock-picking decisions. First, fresh recommendations are more telling than longstanding ones. That is, recent opinion changes tend to have more predictive power than the overall consensus of opinions. Second, "sells" tend to be more prescient than anything else. Analysts who take this rare stance, it seems, often have good reason.

Among thousands of North American companies, just three have at least five "sell" recommendations: Research in Motion (RIMM), whose Blackberry devices are rapidly losing market share for smart phones; Netflix (NFLX), which lost 800,000 U.S. subscribers in its third quarter (see "Bottom Fishing: Netflix Vs. H-P" ); and Genco Shipping & Trading (GNK), a New York City-based dry bulk shipper that some analysts say is in danger of breaching its debt covenants.

Note that plenty of other companies appear to be in worse shape than these but attract lower levels of analyst coverage, and thus fewer "sells". Note, too, that "sell" recommendations reflect analysts predictions for share price declines, and not necessarily deeper financial trouble.

A second search for companies with two or more "sell" recommendations, including at least one issued in the past four weeks, turned up seven names. Two of them have three "sells" apiece: Safeway, a profitable grocer that faces rising competition from Wal-Mart (WMT) and others; and Salesforce.com (CRM), a thriving seller of cloud-based business software whose shares, even after a recent plunge, look pricey at 74 times earnings (see "Is Salesforce.com Worth 100 Times Earnings").

The other five have two "sells" apiece. Sun Healthcare Group (SUNH) is an Irvine, Calif. operator of skilled nursing facilities that faces exposure to Medicare and Medicaid reimbursement concerns but nonetheless boosted earnings guidance this week. Memphis-based Pinnacle Airlines (PNCL) operates regional flights under agreements with Delta (DAL) and United Continental Holdings (UAL) and has recently posted losses. MEMC Electronic Materials (WFR) has been slammed by a global glut in solar wafers and panels.

Insurer Coventry Health Care (CVH) has underperformed larger industry players in recent years, but a Cantor Fitzgerald analyst initiated coverage with a "buy" recommendation in late December, writing that a turnaround is afoot. Finally, Veeco Instruments (VECO) makes equipment used by manufacturers of LED lights. Demand for those is expected to rise over the long-term, but a rush of equipment orders from Chinese manufacturers in recent years has left many with more capacity than they need this year, analyst say.