Presumably you've had different experiences, but from my personal D&D experience I've had zero people who abused the "distress signaling" and seen multiple cases where people were a bit uncomfortable and didn't really say anything other than snarky jokes (e.g. a player's backstory culminates in them graphically torturing an NPC to death while everybody else at the table is weirded out).

"Don't play with them" strikes me as impractical advice compared to communicating. If you're 6 months into a campaign as opposed to establishing a protocol to be able to say "hey this is kinda much for me, could we take the gruesome details of this offline?"

Communicating a tone for the setting early would have also helped.