Well, this was a thread for ideas, and this is just one idea. I understand and appreciate your view point. My comments were simply describing the way some may feel about people who do this. I know it's very apparent how I feel but that isn't to suggest everyone should have the same opinion. Maybe you are right. It's hard to just see a car and then wait around for the owner to come out, yeah, this almost goes without saying it is real work soliciting quality contacts. and I think that just leaving a regular business card doesn't set you apart from anyone else. Having specific cards JUST for leaving on nice cars shows the owner you at least took the time to make up the card.
As far as internet spam, it's a little different then that. Internet Spam would be covering an entire parking lot with your card or a coupon. Not necessarily, Spam hits a certain segment of the Internet. Targeted flyers/cards hits a certain portion of the parking lot (in your case nice cars that are worthy of your services). My point was that it was unsolicited marketing to an address, email or in this case vehicle, something that is all mine. That in my opinion is Spam.
I can see that you do have a pretty passionate stance on this, so I don't want to get into a back and forth with you. Again, it's just an idea. My area is LITTERED with people who call themselves detailers and will go around and flier parking lots on a weekly basis. This way I can show people, "Hey, I don't want to work on all these cars, I want to work on yours." If it works for some people, great. If it doesn't work for others, well at least you are one step closer to finding an idea that does.