Punctuation to denote sarcasm
Does such a thing exist?
I am aware of the irony mark but it appears the backwards question mark symbol doesn't exist in most modern fonts (U+2E2E). That seems to be a good indication of its popularity or relevance, or lack thereof.
I personally use a tilde (~) to denote a sarcastic statement, but I am unsure as to its effectiveness nor can I recall where I learned it.
There is no punctuation mark I am aware of commonly used to denote sarcasm, but one can use other typographic or orthographic indicators.
One can use italics to signify text that is emphasized differently in speech, e.g.
Did you shut the door?
Well, of course I shut the door. We wouldn't want customers to walk in or anything.
Outside of quoted speech, “scare quotes” may suffice.
We wish him well in his new career as a “waste disposal technician.”
Scare quotes can set apart sarcastic neologisms or compounds words, which could also be indicated with hyphenation or capitalization.
The new product line reflects a certain any-color-as-long-as-it's-black-ism among the company's designers.
What better way to close the film's contrived plot than with a Beam Me Up Scotty moment?
Wheeeeeeee! Another season of Idol!
In online chats or other informal communication, one could also employ a range of emoticons, text art, or similar visual tropes.
While it hasn't exactly gained currency, the sarcastrophe is the name given to punctuation used to indicate sarcasm. The humble caret is used to delimit sarcastic phrases ^like so^. You can imply ^^heavy sarcasm^^ through the use of additional carets.
In some circles, the word sarcastrophe is used to denote sarcasm gone wrong.
Then there's the "sarcmark" (^cool name, eh?^) which is an insipid commercial effort to introduce punctuation for sarcasm.
If you're among geeks, you'll often see some form of closing element borrowed from HTML or BBCode used to denote sarcasm - e.g. [/sarcasm] or < /sarcasm>. There's also /sarcasm, which is a reference to IRC commands that needed to be preceeded with a slash. Even though they look visually similar, the /sarcasm reads to me as an indication that sarcasm is being performed, rather than an indication that sarcasm has concluded (as with the closing elements).