Quick:
Is an RX a Lexus, or a Mercedes-Benz? It's a Lexus. What about an XG?* And is the "M" an Acura, BMW, Lincoln, or Nissan? Well, that depends on whom you ask (as explained here, Acura squares off with Lincoln, and here, BMW suing Nissan).

Kim Seung-hyun of the JoongAng Daily tries to clear which alphanumeric name belongs to which brand and how each company arrived at their respective nomenclature schemes. The Hyundai Grandeur L330, for example, refers to its engine capacity of 3300 cubic centimeters. Peugeot use a three-digit naming scheme where the first number indicates the vehicle's make like a compact, mid-sized sedan, etc., while the third number tells what generation it is. Details on the naming scheme for BMW, Renault, and others can be found at the link. Bonus points to anyone that can recall what Merkur's XR4Ti nameplate stands for.

For everyone else who is still confused, be sure to check out our own Chris Paukert's Alphanumeric Soup rant over at TheTruthAboutCars.com for a moment of clarity.

*The XG's, as in XG 30,  XG 300, and XG 350, used to be Hyundai's flagship. The Azera has replaced it. 

[Sources: JoongAng Daily, TheTruthAboutCars.com]