Person at mic end of wireless transmitter has a mute switch.
In corporate gigs that I do, it's common to lock the wireless mic transmitters ON, so that they can't be turned off by accident. And in some situations, the speaker will not want the hassle of controlling their own mute function, they would rather leave tech to the tech.
Personally, I prefer to give control to the person wearing the pack, but some techs do not prefer that at all, and some contracts probably even prohibit it!
I like the idea of optionally latched mute buttons.
ALSO someone mentioned that the slate tone is only 1 second long - it lasts for as long as you hold down the button, so if you need more time to get levels set, just stay on it!