At a company function last week, details irrelevant here, they were handing out temporary tattoos of the corporate logo. We were encouraged to take several, and I discovered over the last few days that people will readily accept a temporary tattoo. Of course, that the company's brand is well-recognized and has strong positive connotations to most people probably played a significant role, but it still planted the idea in my mind.
Some quick research reveals that this is a surprisingly cheap venture. For less that what I paid for dinner & drinks for two last night, I can pick up a thousand or so 1.5"x2.5" temporary copies of my logo. Storage isn't an issue, and apparently they can "stick to almost any smooth surface such as glass, plastic or paint". The image of placing them on windows is particularly intriguing; without skin oils eating away at them, an image will allegedly last indefinitely on the inside of a car windshield.
I've found a few places that manufacture customs, and sent feelers to a couple of them. I think I can have them in hand by the end of the week.