But that’s not all. This vocative form has an extra flexibility that enables you to transform a word in another case into a vocative as well. Let’s take the example above, but change “Paris Hilton” into the vocative form: “@AlexisPetridis, I enjoyed your hilarious review of the @ParisHilton album.” Here, the original meaning is preserved, but the vocative term “@ParisHilton” does an extra job: it tells the reader (and the Twitter system) that the remark is directed at Paris Hilton as well as mentioning her. Paris Hilton can then find it, read it and feel pleased that her album is still fondly remembered, albeit for providing good material for Petridis’s eloquent mockery.
And as if introducing a ground-breaking vocative into the English language wasn’t enough, Twitter features an additional case that I don’t think exists in any other language. I’m going to call this case the referrative case. This is the one that’s formed using a # symbol.
Let’s say you want to talk about Wimbledon; you might say “I bet Novak Djokovic wins Wimbledon!” Here, one might say that Wimbledon is in the dative case, that it’s in that single, catch-all case that most English nouns are usually in. On Twitter, you have the option of using the referrative case and saying instead: “I bet Novak Djokovic wins #Wimbledon!”. This is a way of saying that Wimbledon isn’t just in the sentence, it’s the topic of the sentence; conceptually, Wimbledon is what that sentence is all about. —James’s blog – Lost, lost, lost in a sea of conjecture.