Em dash is a long glyph, which allows to mask several symbols at once. It also looks like a strikethrough and brings some association with censorship. Other than that, it has no additional benefits compared to an asterisk sign (*), or re-phrasing the text in such a way that does not contain profanities.
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence