I've seen the gamut of crosses, rosaries, fuzzy dice, fruit shaped air fresheners, CDs (which are to block speed guns or so goes the urban legend), etc... but panties? What is that about?
A quick change in the car?
A memento of vehicular session of bumping uglies?
An alternative to the fruit shaped air freshener?
Or a spare pair in mindful observance of the advice given by mothers the world over "always have clean underwear...in case you're in an accident"
But c'mon, now - seriously?