Yea I think the issue is somewhere above 7.2.2
Without looking in old posts.
Rick added a feature that you could add a icon to each group.Besides the default moderator and admin. But the user if in multiple groups had to go into their profile and select what icon to display. Since there was no way to determine which icon to display.
The problem appears to be that now the M becomes a group icon.
So if selected in the user profile it will appear in any post in any forum regardless if they are a moderator or not of that forum. It shows if they are in a moderator group even if they are not the moderator.
So the only way to turn it off is to completely delete the icon or deselect it in the user profile.
I never gave it much thought.
But I guess it can be deceiving to someone visiting a topic and see the icon and think they are the moderator of that topic when in fact they are not.
