Humans express social status in many ways. We show our submission to others by deferring to their wishes, copying their styles (e.g., dress, speech), praising them, laughing at their jokes, and so on. We show our dominance by expressing desires, styles, jokes, etc. and then expecting others to show submission.
Our opinions are part of this dominance/submission signaling system. The higher we feel in status the more we feel free to express distinctive opinions and expect others to agree, or at least not greatly disagree. Which is why we are so reluctant to agree with others we compete with, even when they make good points.
Drivers of cars with bumper stickers, window decals, personalized license plates and other "territorial markers" not only get mad when someone cuts in their lane or is slow to respond to a changed traffic light, but they are far more likely than those who do not personalize their cars to use their vehicles to express rage — by honking, tailgating and other aggressive behavior.
It does not seem to matter whether the messages on the stickers are about peace and love — "Visualize World Peace," "My Kid Is an Honor Student" — or angry and in your face — "Don’t Mess With Texas," "My Kid Beat Up Your Honor Student." … Aggressive driving might be responsible for up to two-thirds of all U.S. traffic accidents that involve injuries. … Drivers who do not personalize their cars get angry, too, … but they don’t act out their anger. ….
Drivers who individualize their cars using bumper stickers, window decals and personalized license plates, the researchers hypothesized, see their cars in the same way as they see their homes and bedrooms — as deeply personal space, or primary territory.
Added: As an analogy consider the strut. It is clearly a dominance signal, even though the rich may strut less than the poor. And if people around you think your strut is reaching above your status, they may severely punish you.