English orthography does not include a sarcasm punctuation mark. Many languages have an irony or sarcasm mark. For English, the SarcMark was recently created and marketed, but you have to pay to get the software to use it.
What we need is a punctuation mark that is directly available on keyboards, but would be unambiguously evident when used for sarcasm. Also, it needs to be seldom used in normal writing. I propose that the tilde [~] be used before and after the word or phrase that is intended to be ~snark~.
What do you think?