That works too! I got to thinking too, my idea would get complicated. My idea v2 lol........I think just organizing the "re-order rigs" section so that the top 3 ARE your sig rigs and that's its own separate area to organize in would probably work the easiest long term, and just doing away entirely with the buttons to show / hide in sig. That way users can just drag them out of their sig in the reorder part. If that separated section is empty, you've hidden all rigs from sig. If there's only 1 rig up there, then you're only displaying 1. And then in your list of rigs, they'd all show up in that same order. If that makes sense. So rigs 1-3 are automatically "sig rigs", but if 1-3 (or 2-3 or whatever) is empty, the ones in spaces 4+ just move up a spot in the list in settings to compensate. I wouldn't THINK that would be too terribly difficult to code since the breaks, borders, fonts and everything are all already there. It'd just be a matter of getting the "settings" page (before the reorder) to cooperate nicely if the "sig rigs" section isn't fully populated.
Kinda like this, and you could edit the titling to reflect it with the same fonts as the "Drag and drop your rigs to sort...." so that its more clear than my poor MS Paint job.....
This would do away with the buttons in the settings page entirely, and the confusion.
As is, what you've done definitely helps a TON to realize which ones are shown and which ones are not though. Just trying to help streamline the whole process with ideas is all. I'm sure you've probably already got something better in the works anyway.