Here is a new one to me.

I am using 2018 SP4. I have been working in an assembly adding components in different configurations and such and this morning after several days of working I see a new icon show up in the configuration list. Everything seems to be working fine and I have saved the model both with the configuration active and not active but the icon is still there. I did not find a reference to it in ​'s stickied FAQ either. Does anyone have an idea what it is for?