Yes, people have been trying to find ways to denote irony for hundreds of years. In 1688, John Wilkins, the Bishop of Chester, wrote an essay called An Essay Towards a Real Character, and a Philosophical Language, where he attempted to help develop a new "universal language" to replace Latin, which had been coming under criticism for being difficult for people to learn. He envisioned his new language being used by diplomats, academics, and merchants as a new lingua franca. One of the things he suggested in this essay was the use of inverted exclamation points to denote ironic statements.

The lack of ability to denote irony was also considered to be a problem by some French intellectuals, notably, by Rousseau, who wrote about it in his Es­say on the Ori­gin of Lan­guage. In 1841, Marcellin Jobard, a Belgian newspaper editor, made his own attempt at fixing the problem and introduced his own irony mark, an arrowhead with a small stem. In France, a poet named Alcanter de Brahm created his own "irony point", which I honestly don't know how to describe in a way that's easy to visualize, so I'll just [link a picture] (https://en.wikipedia.org/wiki/File:Point_d%27ironie_de_Alcanter_de_Brahm.svg). Jobard and Brahm both also suggested other punctuation marks in addition to their irony marks in order to help readers discern tone (for example, Jobard created one to express annoyance). None of these marks really caught on.

In the 20th century, a few more people made attempts. Hervé Bazin, the French author, designed yet another mark in the 1960s, which he included in his essay, Let's Pluck the Bird, along with marks for doubt, love, and conviction. Finally, a man named Tom Driberg, a British journalist and politician, came up with the idea for "ironics", which were italics that leaned left instead of right and were meant to convey irony. Driberg and Bazin's ideas both more or less went ignored. The only grammatical way of conveying sarcasm that seems to have had legs is the use of scare quotes. For example, a pre-Internet person might write in a letter that they had so much "fun" hanging out with their mom, implying sarcasm.

But ultimately, while a lot of people believed the lack of a clear way to signify irony/sarcasm in writing was a problem, none of the proposals to fix it have really caught on. In 1999, a group of linguists pushed UNICODE to include a Temherte Slaq, an Ethiopian character denoting sarcasm, in its library of characters, but that's been about as unsuccessful as anything before it. So while there were some obscure ways to denote irony/sarcasm in text before, the /s and emoticons like :P have been the most widespread and successful.