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 auto parts dealer Dorman Products (Nasdaq: DORM) fell 10% today on news of insider sales.

So what: CEO Richard Berman and his brother -- president and director Steve Berman -- will sell up to 250,000 shares each. CFO Mathias Barton will also sell 25,000 shares, so insiders aren't giving the market a good signal today.

Now what: Insiders selling can be a bad signal for the future performance of a stock, and when everyone is running for the hills I get a little worried. Both Bermans are selling a big portion of their shares, so they must not think the company can keep crushing estimates like it has for the last year. At the risk of going along with a panic sell, I don't see this as a good sign for investors.

Interested in more info on Dorman Products? Add it to your watchlist.

Fool contributor Travis Hoium does not have a position in any company mentioned. You can follow Travis on Twitter at @FlushDrawFool, check out his personal stock holdings or follow his CAPS picks at TMFFlushDraw.

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 Motley Fool has a disclosure policy.