There are a few punctuation marks that can be used to indicate sarcasm, including:
Exclamation mark in brackets: For example, "Oh, really[!]", this is similar to how a bracketed question mark can be used in informal rhetorical questions.
Tilde: A tilde (~) can be placed next to punctuation to indicate sarcasm. For example, ~. for dry sarcasm, ~! for enthusiastic sarcasm, and ~? for sarcastic questions.