ESSB and the + sign on the front panel display

Doug, VE3MV

I’m having a memory lapse - recently there has been a “+” sign in the bottom RH corner of the K3 display. What does it signify (perhaps ESSB ??) and how do I turn it ON or OFF. I’ve checked prior messages on GroupIO but so far unable to track it down.

Tnx & 73
Doug VE3MV

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