Even if McDonald's were being total dicks about Supermac's, the remedy shouldn't be for the Government to act like a petulant child.
If "everyone knows McDonalds sells Big Macs" is a good argument then it shouldn't be hard to find evidence that it indeed is so. It wouldn't have been hard, McDonalds just didn't bother to provide that for some reason.
If a small, young company would try to defend their trademark nobody would believe them even if they printed brochures, menus, and told "yes, we really really really do sell these". There's nothing of substance in such claims. Printing is cheap.