I think the most basic safety tool is informed consent, whether it be in an RPG, traditional board game, or kinky bedroom games. Should that have to be stated in the rules? The idea seems odd; who would play a game they did not want to play? The answer of course is sometimes we agree to or consent to a game that we did not have all the information for.
A good example of informed consent was the Industrial Arts teacher who ran the Strategy Games club in my Middle School. Day one he explained to us in detail (those of us who were new) what Diplomacy was and was all about. So when I got backstabbed by Russia, I was not surprised or that upset. I understood that Diplomacy was that kind of game.
Uninformed consent was when playing a different game (Axis & Allies I think) members of the teams turned on one another. I was a bit boggled by this and did not play with these people again, Apparently this was a common occurrence with this group.
So I think at the very least, when designing a game the designers can and should be explicit about what kind of game the players are getting into. Super casual or some kind of super betrayal Cyberpunk variant where the goal is to succeed in a mission but be the only character to survive and gain experience. Then it is up to players to decide for themselves if that kind of game is for them or potentially so.