Bloomberg notes that just 5.1 percent of analyst ratings are "sells" and that of 1,890 analysts, fewer than 1 percent advised unloading a Standard & Poor's 500 stock that either later showed a decline, or rose only after they upgraded it.

There once was a day when critics pointed to the dearth of sell recommendations to suggest that sell-side analysts were either cronies to the deal makers or just not up to snuff. In a bull market after the separation of research from deal-making, it's harder to make that case. To be frank, the 5.1 percent share may not be historically all that low.

These days, sell recommendations are so rare that they stand out in the crowd. People take note. And that presents a decent opportunity for sell-side analysts. You can really burnish your reputation if you are right.

Bloomberg takes a look at a few cases, including the case of Adnaan Ahmad, a London-based analyst at Berenberg Bank, who was correct when he initiated  coverage of Motorola Mobility with a sell call.

You have to be really careful as an analyst. Such calls tend to generate controversy--the issuer is never happy--and if you are repeatedly wrong, you will undercut your credibility. So if you are going to call "sell," you had better be right.

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