From that pic, it appears that the screw is merely clamping the visor in place, possibly going partially into the visor, but not through the helmet itself. The reason I say that is because if the screw was going all the way through the helmet and say cut off and puttied over, why wouldn't they have screwed the screw all the way flush to the visor rather than leave the gap between the two? Wouldn't the visor would be flapping back and forth?
The bracket is more than likely just epoxied to the helmet. This would make for easy replacement of a cracked visor without having to rip out any glue although I would consider possibly spot gluing a few areas (ends of the 'T', where the 'T' starts to go downward, and at the very bottom) just for a little insurance. I haven't installed the visor in my "movie size" helmet yet, so some collective opinions would be nice.