Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of coal producer International Coal (NYSE: ICO) plunged as low as 16% in early Tuesday trading on news that two of its largest shareholders plan to sell nearly 35 million shares of the company.

So what: Unfortunately for International Coal bulls, the unloading whales are none other than Prem Watsa (through Fairfax Financial) and Wilbur Ross (through WL Ross & Co.), two of the smartest stock sharpies around. Each investment great will continue to own about half of their respective stakes, but International Coal's hot stock price, coupled with today's news, has Mr. Market questioning just how much fuel the stock has left.

Now what: I'm a believer in following the smart money, so I'd be inclined to stay away from International Coal right now. While the stock sales aren't dilutive and International Coal's total number of outstanding shares will not change, I'm interpreting the news as a signal that the stock's 100% return over the past year is simply overdone. Watsa, of course, is most famous for making Fairfax billions in a big bet against the U.S. housing market, so I wouldn't exactly want to be buying what he's selling.

Interested in more info on International Coal? Add it to your watchlist.

Fool contributor Brian Pacampara owns shares of Fairfax. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Fool's disclosure policy always gets a perfect score.