Mute the mic, un-mute the mic. Handy for recording or live talkback stuff, although I'm sure you can think of other times too.

Model: ProCo Sign Off Power Mute 
Made: USA, recent model
Serial: 703272076291
Type: master mute
Power: standard 9v DC negative power supply (not included)
Equivalent New Street Price (Approx): $299aud
Mods: none
Accessories: none

Condition Notes: used, no major marks. Tested and fully functional.
Overall: excellent condition (9/10)