It may look like an archaic typo, as if a typewriter got bumped mid-sentence, but no, the combo exclamation-question mark is a real punctuation mark. The interrobang was invented in 1962 by Martin K. Speckter with the intention of allowing advertising copywriters to convey surprise in rhetorical questions.
I like to remember the name of this glyph in the context of an interrogation, a heated one, with questions like, "And does this mean anything to you?!" while a gristle-faced cop thrusts the damning evidence in your face.
Interrogatio is Latin for "a rhetorical question" or "cross-examination" and bang is printers' slang for the exclamation point. (Is that still true? I just learned that in my research this morning. If you're a printer and use "bang" let me know because I don't want to miss out on an opportunity to say bang!)
Not a lot of fonts have the interrobang – Helevtica does, Palatino Linotype, some Unicode fonts and I really hope there are others that I haven’t found. There's even an interrobang advocacy group on Facebook!