Trouble is, non-gotcha traps don't make sense. The literal point of the trap is for it to go undetected so that it catches the target unaware so that it can inflict pain, suffering, and even death on whoever stumbles into it. Signposting a trap negates the literal point and purpose of there being a trap.
The two most famous examples of traps in modern times, I think, are Raiders of the Lost Ark and the Vietnam War / Resistance war against the US. In the first, Indy knows there are traps so is careful and intentionally triggers one to show the audience there are traps. The whole temple sequence of the movie is one long trapped dungeon. In the second, the Vietnamese used guerilla tactics and a wide variety of traps to resist the US. In neither case were the traps signposted to give the targets a "fair" warning*. Because that would literally defeat the purpose of the trap.
* Unless of course the signpost was itself part of the trap. Here's an obvious trap, pay attention to this obvious trap while you are hit with this non-obvious trap. The angler fish trap, as it were.
So would the referee saying, "All dungeons have traps" be enough? Or, "This game features traps" be enough?