Proposals for an irony punctuation sign have been around since late nineteenth century. Stylistically, I prefer this relatively recent Dutch proposal¹.

But, as noted in the wikipedia articles, some feel that explicitly indicating when text is meant ironically defeats its purpose; irony is supposed to make you think.

1: The 'Het ironieteken van de CPNB' one the right: https://nl.wikipedia.org/wiki/Ironieteken