you post a picture of your car on your friendster/myspace/facebook/etc. page. Seriously.*
And I particularly enjoy the people who post pictures of their really old, beat-up, P.O.S. cars just because they happened to paint a lame racing stripe on it or they put a huge spoiler on the back of their Honda Civic. News flash - Honda Civic's do not need a 3 foot high spoiler.
*Unless of course, you are a certain A. Hill who needs to post a picture of her kick-ass '92 buick. Pronto.