How to Not Design a Car Window Sign

So while driving today, I saw a car with a rear window ad. It was colorful and presumably informative. Sorry, I don't have a pic - camera was in the trunk. But it was full-coverage white background like those from http://www.infowindow.com/.

It had the phone number in large black type. Good.
Company name was in 3 colors, as was the URL.
There was also an eye-catching graphic in the design.
Would have made a terrific business card.

As a window ad or billboard design it was useless:

• In the sun, the yellows used in the URL faded into the white background.
• On the road, people aren't going to remember a phone number. Feature the company name or memorable URL.
  
• The company name also got lost due to contrast. It was too small and the glare off the window hid all the light-colored elements.

Technorati Tags: design, advertising, signage, automotive, billboard