Yes, people actually tried to patent and sell a punctuation mark called SarcMark so that you could indicate you were being sarcastic in written form:
http://www.thedailybeast.com/articles/2013/09/24/the-rise-and-fall-of-the-infamous-sarcmark.html
Here's the actual website for the company:
http://www.sarcmark.com/
And of course there's an Open Sarcasm project against charging people for using a punctuation mark to convey sarcasm:
http://opensarcasm.org/
...
It all seems like it should be one giant sarcastic argument against trademarking language and punctuation, but unfortunately it looks like it's actually all true and serious :(
I always feel weird when this subject comes up because it feels like sarcasm is something that requires the writer to be proficient at and the reader to be able to understand. Both writing skill and reading comprehension fall into play, which are in short supply online, so I understand the intention behind it but adding a flag to indicate sarcasm feels like adding a laugh track to a sitcom to me, like the producers aren't confident that their writers content is actually "funny" so they add cues for the "dull" audience.
Maybe it will catch on as well as the interrobang did‽
;-)
[/sarcasm]
or simply
/sarcasm
/thread.