There's no button on Linux, but who needs one? This skill teaches Mycroft a handful of dismissive terms, in case you should change your mind after speaking the wake word.
This skill includes a setting "verbal_feedback" which, if set to False, does exactly what it sounds like, enabling you to dismiss Mycroft silently. However, I have not yet implemented a way to toggle that value, so verbal feedback is always on.
Platform:
Mark I
Mark II
Picroft
plasmoid
Examples:
Nevermind.
Dismissed.
Forget it.
Go away.
Installation:
This skill is not aproved by Mycroft skill tester.