These do exist, but you never have to pay them... They pay you...
The sites that ask you you pay them $9.95 to $29.95 to get on some list are a scam... These sites simply submit your info the real sites for free...
Here is an example of a legit site:
AdSmart Outdoor Advertising - AutoAds - Drivers
Note that they will not charge you a penny to get on the list...
Also, keep in mind that you may not be able to park your car as easily anymore. In my neighborhood, vehicles with any kind of 'branding' are not allowed to be parked overnight on the street, driveways, etc. So, it would have to be parked in a garage or under a tarp at night. One of my neighbors has a 'tuner' with appropriate sponsor vinyls and frequently gets fined/towed because he forgets to garage/tarp his car (his own fault though -- he is constantly 'showing off' his ride and too lazy/drunk to pull it into his otherwise empty garage at night).