Nothing new under the sun: https://en.wikipedia.org/wiki/Irony_punctuation

I would not say we need tag or symbol. First of all it was not sarcasm at all, just a plain joke. And second, instead of a symbol, what we need is to read more books.

if "my God" part wasn't evident, and you need a mark for sarcasm/joke/take the piss... I guess that part is beyond help