Yep. That would be the point of non-verbal safewords. You want to gag someone? Cool - but give them a bunch of keys to drop or a bell to rattle. There are plenty of "safewords" you can use, and you tailor them to your personal situation and scene.

(I'm speaking as an occasional dom and hard-of-hearing person. It's something I've put a lot of thought into because I'm at a slight disadvantage to most folk when it comes to hearing safewords. So we work around that.)