Bo,
Cell cast acrylic, or PMMA (polymethyl methacrylate), is a shatter resistant plastic. According to Wikipedia, it has been used for such things as the windows of submersible submarines, police riot shields, transparent shields at hockey rinks, lens for automobile headlights, the transparent dome of the B-17 flying fortress, and the roof of the Astrodome. It is used for aircraft windows. In fact, Lexan is not accepted for aircraft windows because in case of a necessary rescue, it cannot be broken. Although I don't think this is a big issue for open or partially streamlined motorcycles, I'm not sure I would even want lexan for the windshield of a streamliner. If they couldn't get the door open, they wouldn't be able to rescue the driver! There should be no question of its acceptance as a shatter resistant plastic. I might add that it would difficult to police the issue in any case, as I'm not sure there is any way to tell the difference with a non-destructive test.
Tom