While I like the idea of a bubble, that shows anytime you're typing - regardless of teamchat or public (because you can't use the bubble as justification). I'd rather something more discrete like a couple animated dots (kinda like on Discord when someone is typing). And as others have said, it could be opt-out, if you're opted out you can't see when others are typing and they can't see if you're typing.
Didn't intend for it to specifically be a bubble shape or anything so I changed the title to not throw people in the wrong direction.
How about instead of putting a notification above their head, you put it on their body? Such as a small bubble on their chest and back? Takes care of all concerns of cover, etc, right away.
But I thought the concerning issue was the point that you would know the person was typing and take advantage of that knowledge and kill them?
I was more-so addressing the concerns about cover- but I do think my alteration to the idea would make it a bit more conspicuous as it's not as blaring as a bubble over someone's head. Maybe those concerned about it may be able to get behind it?
A DarkRP server I used to play on had this, so it's definetly possible. They used the commentary chat bubble prop thing and just had it rotate over the individual's head.