Mercedes-Benz has worked its way through a good chunk of the alphabet to name its various product lines, but it hasn't used up every letter just yet. In fact, according to the latest, it's just registered to trademark a new one. We just don't know what it could be for.

AutoGuide reports that the German automaker has filed to protect the name O-Class and several derivations thereof – including an O 120, O 140, O 180, and O 200. And our best guess is that it could be for some kind of bus or van.

Daimler's commercial-vehicles division sometimes labels the Citaro city bus as the O530, and previously used similar names like O319 and O405. The numbers registered this time, though, indicate smaller engines, like you might find in the A-Class, B-Class, CLA, and GLA.

Could we be seeing the first indication of a new minivan, then? A passenger version of an existing commercial vehicle? Or something else altogether? And will that model be sold in North American passenger-car dealerships? The only additional information we have is that the name is intended for use on "motor vehicles and motor vehicle engines."

With so little to go on, we're left with more questions than answers, but, we're definitely intrigued.

Currently Mercedes sells classes of vehicles represented by the letters A, B, C, E, G, S, V, and X. It previously used the letter M for the precursor of today's GLE, as well as another minivan/crossover/wagon called the R-Class. The rest of its models use longer alphabetical designations like GT, CLS, and EQC, while its commercial buses and trucks carry nameplates like Citaro, Sprinter, Unimog, and Zetros.