I'm hoping someone can shed light on the purpose of this annunciator. I've flown this airplane a fair amount and have never seen it illuminated before today's trip. I've been through the documentation but don't see a description of what it is indicating and how to extinguish the light. I'm currently 3 hours into the flight and haven't noticed any particular consequence of its illumination, but as I understand the Boeing philosophy of no lights in normal operation, I really don't like seeing any...especially red ones... ;)