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.