I think it's a cup-of-tea-ometer.
You know, when you've been tweaking longer than you should have, the LED pops on as if to say "Take a break and give my knobs a rest, you complete geek!". When it starts flashing you know you're in for trouble, as the synth's chassis auto hooks up to the mains electrics via an electronic relay, and zaps ya silly next time you prod it.
PS > Thanks Marc.
