The MFC has all class names that start with C. For example, CFile and CGdiObject. Has anyone seen it used elsewhere? Is there an official naming convention guide from Microsoft that recommends this style? Did the idea originate with MFC or was it some other project?
Something a bit similar is used in Symbian C++, where the convention is that:
T classes are "values", for example TChar, TInt32, TDes
R classes are handles to kernel (or other) resources, for example RFile, RSocket
M classes are mixins, which includes interfaces (construed as mixins with no function implementations). The guideline is that multiple inheritance should involve at most 1 non-M class.
C classes are pretty much everything else, and derive from CBase, which has some stuff in it to help with resource-handling.
HBufC exists primarily to generate confused posts on Symbian forums, and having its very own prefix is just the start. The H stands for "huh?", or possibly "Haw, haw! You have no STL!" ;-)
This is close in spirit to Apps Hungarian Notation rather than Systems Hungarian notation. The prefix tells you something about the class which you could look up in the documentation, but which you would not know otherwise. The whole point of naming anything in programming is to provide such hints and reminders, otherwise you'd just call your classes "Class001", "Class002", etc.
Systems Hungarian just tells you the type of a variable, which IMO is nothing to get very excited about, especially in a language like C++ where types tend to be either repeated constantly or else completely hidden by template parameters. Its analogue when naming types is the Java practice of naming all interfaces with I. Again, I don't get very excited about this (and neither do the standard Java libraries), but if you're going to define an interface for every class, in addition to the interfaces which are actually used for polymorphism in non-test situations, then you need some way to distinguish the two.