Ask the Reader: CD's as Car Decorations?

On the way to and from dropping off my daughter at school, I noticed more than a couple of cars having CD's hanging on strings from the rear view mirrors.  To borrow from Seinfeld, what is the deal with that? 
Could it be:

• that people have an emergency CD handy in case the radio is glutted with awful music (Wham, Duran Duran, Tragically Suck, etc.)?
• that people carry around their backup disk at all times in case their hard drive crashes or is stolen?
• that they hope to blind potential pursuers with multicolored reflections?
• that they hope to hypnotize passengers while the CD sways back and forth?
• that they can yank it off the thread and throw it at a zombie?