Given that things like tone that are normally used to show sarcasm dont show through text, the only way if one doesnt explicitly state something to be sarcasm to tell if something written is sarcastic is if the statement seems so absurd or obviously wrong that nobody could seriously believe it. However, people have a seemingly limitless capacity to believe things that are factually untrue, and what is and is not absurd is to some extent in the eye of the beholder, so ultimately, one should not be surprised if one’s written sarcasm is taken seriously, if you dont include some kind of signifier to replace the cues normally given in speech.
Given that things like tone that are normally used to show sarcasm dont show through text, the only way if one doesnt explicitly state something to be sarcasm to tell if something written is sarcastic is if the statement seems so absurd or obviously wrong that nobody could seriously believe it. However, people have a seemingly limitless capacity to believe things that are factually untrue, and what is and is not absurd is to some extent in the eye of the beholder, so ultimately, one should not be surprised if one’s written sarcasm is taken seriously, if you dont include some kind of signifier to replace the cues normally given in speech.