What do the four yellow dots mean that are below the avatar? I noticed one of mine lit up.

The dots light up as you progress through the ranks.

If they seem vaguely familiar to your from somewhere, you will all smack yourself as I now reveal that they are the collar pips from Star Trek TNG.

Notice that as Administrator, I have given myself the 4 pips with a bar around them, which is the Admiral's insignia. Mine stay that way from day one, but for the rest of you, you can delight as you progress from Ensigns to Captains and beyond.

Star Trek! I didn't expect that. So what rank is each of the four lights? And what would happen after the fourth?

To go where no kurkikohtaus has gone before........

I can't remember exactly at which ranks the pips increase...

There are more ranks than actual pips, so your rank may increase but your pips may stay the same.

"Go where no K. has gone before..." Nice.