It's possible you're thinking of:
* Sarcasm: This is often conveyed through tone of voice, but sometimes writers use punctuation to indicate it. Commonly, this is done with a single question mark at the end of a statement, like: "Oh, you're just *wonderful*.?"
* The "deadpan" effect: This involves using a flat, neutral tone of voice to deliver a statement that's actually meant to be ironic or sarcastic. The lack of emotion in the delivery makes the irony more pronounced.
* Figurative language: Irony is often conveyed through figurative language like understatement, overstatement, or paradox. Punctuation isn't specifically used to mark this kind of irony.
It's important to note: Punctuation is a tool used to clarify the structure and meaning of text, but it doesn't inherently convey irony. Irony is a literary device that relies on the reader or listener understanding the intended meaning in contrast to the literal meaning.