Rolling Probable Cause??
I realize that modern day bumper stickers are all about expressing individualism. To get reactions out of other drivers. Think about the last bumper sticker you saw featuring the name of a candidate for public office (who you wouldn't support even if hell did freeze over).
But would you display a bumper sticker like the one in the photo above?
The lawyer in me says that this form of expression might well be reasonable grounds (sorry for the legalese) for the constabulary to conduct a traffic stop.
(In this instance the vehicle's identity has been concealed to protect the potentially not-so-innocent.)