So what are those yellow squares under our names about?

[Call Me Cordelia]

They seem sort of random. No explanation. Not apparently tied to post count... What are those little yellow squares??? I've been on here for a couple of years and I just never really thought about them. 

[Spring Butterfly]

It's a group color code so hosts are yellow and mods and admin are other colors. They also show up in the forum homepage at the bottom where whoever is online is listed