If we see a script modified on-disk, assume the user is a script author. If so and there is no @grant metadata (so it gets sniffed), throw some sort of warning at the user.
Ideally, with https://developer.mozilla.org/en/Using_popup_notifications if we also make minversion==4.0 in this release. Where actions would be to open detailed (wiki) documentation, and dismiss future warnings like this.
Notify upon modifications when scripts are missing @grant.