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: According to Warren Buffett, there's no better indication of the health of the U.S. economy than the health of its train business. That's bad news for the U.S., and worse news for investors in railcar builder Trinity Industries (NYSE: TRN), which reported earnings last night ... and is down 10% today.

So what: Trinity earned $0.37 per share in the second quarter, or a penny shy of Wall Street's prediction. That was the bad news. The worse news is that in the current third quarter, Trinity is only promising to earn about $0.35 per share -- a full dime short of Street estimates.

Now what: In the best case scenario, Trinity now thinks it might finish up the year with $1.45 per share in profits. If that's how things play out, it would equate to a 22 P/E ratio on the stock -- a pretty penny to pay for 10% long-term growth. Worse still, Trinity warns it could earn as little as $1.35 per share this year. And did I mention the company also carries $2.5 billion in net debt -- a sum fully as big as its own market cap?

If you ask me, investors are doing exactly the right thing by selling off this overpriced maker of oversized Lionels. And I wouldn't advise hitching your fortunes to Trinity, either.

Disagree? Think this little engine still can? Add Trinity to your Watchlist and see if you're right.

Fool contributor Rich Smith does not own (or short) shares of Trinity Industries. 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.