I suspect this may have been asked before or addressed somewhere in an FAQ but I’m too lazy to look so I’ll just ask:
What does the green light/spot next to many usernames (including my own) mean?
Mouseover.
“kidneyfailure is online now”
Ohhhh…that makes sense. I feel like a moron now.
No, no… morons get a different color light.
Grey is offline. Red is invisible (i.e. user has disabled online status display).
Do other people’s circle show red? I thought it only showed red to yourself.
Only Cecil/Ed could test that. It’s the only sock account. (Not intended to disparage, but merely to inform.)
Other posters don’t see it. Staff members do. It’s a terrible burden. 
nm
I think the green light is supposed to represent Gatsby’s everlasting but impossible dream of being with Daisy, the one he loves - it is all of our hopes and dreams, all of the things that we believe in even though we will never reach them.
