As part of acknowledging a trigger, the accountable player must communicate the trigger to all other players in an understandable and observable way. Examples include verbally announcing the trigger, physically indicating the trigger, or other means of communication understood and agreed upon by all players in the game.
§ 506.3.a Tournament Rules PDF (officieel)
§ 506 Triggered Abilities
§ 506.3 The accountable player must acknowledge their triggers by the time they would have an observable impact on the game. If they do not, they are forgotten.
