A friend of mine years ago had all four of her tires flattened and a note on her windshield taking exception to the candidate bumper sticker on her SUV.
But that was a Senate parking lot, where peops tend to be more partisan than the nation at-large.
I've never seen the point of alienating two-thirds of other drivers by displaying my politics on the car. Could make it harder to merge.
Dog and national park stickers, yes. Those are nonpartisan.