http://www.leftlanedrivers.org/default.html need the cycle helmet sized... but it'd be too small to read.
I heard about this a while ago, the guy who makes em had one on his car and said it gets results. It would be interesting to hear what happens on a 2 lane road though, I know that in Texas(at least south central, San Antonio and points surrouding,) it is customary, practiced that slower drivers, even on a two lane road to move into the shoulder, and let faster moving traffic pass, but, I dont know if there is a law that allows or prohibits it.