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 local-advertising specialist China MediaExpress Holdings (Nasdaq: CCME) are up by 11.3% and counting on modest trading volume this morning.

So what: The company enjoyed a quick short-squeeze episode in mid-November, but the joy was short-lived and prices came spiraling down. Today, analyst firm Global Hunter Securities upgraded the stock to a buy on the basis of a more attractive valuation than before.

Now what: China MediaExpress has carved out a unique niche by placing ad-blasting TV screens on intercity buses in Beijing. The stock trades at a very reasonable seven times trailing earnings and a PEG ratio of just 0.27, so the valuation-based upgrade makes a ton of sense. Just tread lightly, because there can be dragons around this company. It's a small-cap with a strong balance sheet and very little competition, but the operating history is short and it's tough to get a feel for how profitable the bus-based marketing niche might be on the other side of the world.

Interested in more info on China MediaExpress? Add it to your watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. 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 is investors writing for investors.