Showtime Glass is a tempered glass screen protector for iPhones. It has embedded glitter that "sparkles in any light condition" but is not visible when the display is on.
http://www.notebookcheck.net/Glitz-and-glam-on-the-go-MOXYO-Showtime-Glass-adds-sparkle-to-your-iPhone-s-screen.198072.0.html