1. Vehicle magnets: Cost about $20 each. Good for a basic message. I think I get about 1-2 calls a month from mine (3 sides of the truck) for home improvement services; well worth it so long as your SO doesn't mind.
2. Vehicle wrap: Really makes a vehicle stand out. The problem is the cost: $3,000 - $7,000 or more depending on the type of vehicle. Does the cost justify an increase in response? I don't know