OK.
Let me add a wrinkle, then. Let’s assume our cops are zealously neutral. They issue a ticket regardless of what stickers a car might have. But they respond to reckless driving, and the respond to citizen complaints.
Now let’s assume I live in Dallas.
In Dallas, many people are around who dislike the Redskins and are willing to report me for minor speeding violations. In response to those reports, I get ticketed. But the Dallas Cowboys fans, driving around in Dallas, are not at the same risk, because there are so few hostile Redskins fans to report them.
So the police, here, are acting without bias. But the environment is biased.