Adding a custom BBCode to a forum adds a button above the editor but it just shows the BBCode tag text in the button and there's no option to add an icon.

It would make the UI look much nicer if admins could specific a custom icon for the BBCode button so it matches the other default BBCode buttons above the editor.

This would work as a small extension, but it seems like a nice little addition to core that would be a welcome addition for people, right?