I myself think "+/-" would be a good symbol to represent polarity switch.
Not bad, but I haven't designed a console in this century, I haven't even touched one.
If I was still in the game, I'd test that... I vaguely recall playing around with a symbol that was one cycle of a sine wave with a + inside the positive half, and a - inside the negative half. Or perhaps two sine wave cycles one starting with the up half, and the other starting with the down half.
The worst thing you can do is confuse the operators when they are looking for which switch to throw a mic out of phase with another..
I would gladly use the word "phase" if it wasn't for pedantic whiners (like me) who know it should be polarity.
The customer is more right than the seller.
JR
PS: I got the design problem sorted.... when i tried to write an email to send mike, my subconscious was apparently embarrassed and gave me the solution it apparently was sitting on.