
As always, I have not done a patent search or extensive research, but I did search the web for a while in an attempt to find something similar to the product/advertising technique that I am about to propose. The closest I came was Scott Wade's site DirtyCarArt.com which is where I got this beautiful rendering of Albert Einstein.
Here is the invention.
Sponge stamps of logos or website addresses that you can use to print on dirty cars with, and guess what, I actually got up from my computer and made a prototype to show my billions of beautiful readers that it can be done.

This is just an over-glorified felt cloth from OSH stapled to a piece of wood. It works fairly well. The important thing with this is not to use material that can hold too much water. I am sure that by spending more than the half an hour I spent putting this together, some of you giant corporations that have been tracking my blog or some of you Banksy apostles can come up with something much better. Maybe you can even build some sort self wetting mechanism into it like this kitchen dish brush.

You might want to look into making the stamp out of cat feet, since they seem to work very well. Just kidding.
Here is the advertising.
Either produce a sponge stamp in mass quantities and give it out to tons of little kids under the guise that they are for something else, while sending out some street teams to sponge cars around schools in the areas that you have given out the sponges to plant the idea in the kids' minds, or just send out street teams to hit up urban areas that you want to hit. Car washes should really take notice of this idea.
I know some of you are asking yourselves why I don't just take this idea and actually sell it to someone, or start a company to produce these sponges. I took the time to make a prototype etc. Why don't I actually do something with this idea? I considered it, but it is something that is so easily replicated in so many different ways, and there is a possibility that it already exists. I would have to do a patent search. Costs money. I would have to patent like a hundred variations of the design. Costs money. Then I would have to sue every street kid with a pair of scissors and the ability to make a stencil. Where do you think that would get me? The product is a bust by its self. The marketing is where it is genius.

P.S. Subscribing to Ideas By Chuck is good for your soul.
P.P.S. I have received some positive support from some fairly mainstream media outlets besides TBTL.
Gawker writeup
NewYorkPost.com
P.P.P.S. Only use the car sponge stamp on windows. Using it on the actual car could mess up the paint, and people will get mad.
P.P.P.P.S. I welcome any logo ideas for Ideas By Chuck. Also, feel free to make a car sponge stamp for Ideas By Chuck and go around stamping dirty cars with it.