From Jonathan Lundell, a pointer to a posting on the Canadian Design Resource site yesterday:
According to The Week [of October 8th], in 1992 a patent was filed here in Canada for these two alt punctuation marks: the “Exclamation Comma” and “Question Comma”. Presumably, each mark would express enthusiasm or inquiry respectively at a time when the user was not yet prepared to end the sentence.
The Week lists a number of other alternative punctuation marks:
in 1966 French author Hervé Bazin proposed [an irony mark] in his book, Plumons l’Oiseau, along with 5 other innovative marks
See Ben Zimmer’s Language Log posting “Punctuation, now with heightened indifference!” for more discussion.
Two alternative marks have gotten the most attention: the percontation mark and the interrobang.
The percontation point (a reversed question mark) indicates irony or sarcasm. The interrobang (a superimposition of question mark and exclamation point, or the two in sequence: usually ?! , sometimes !?) combines interrogativity and emphasis. (For the contrast between the exclamation point and the interrobang, see my discussion of a Bizarro cartoon here.)