If you make bumper stickers, please make them so that the background is clear. The CleanMpg ones have a white background, which I think makes them too prominent. I would prefer if just the text shows up.
If everyone wants a clear background, wouldn't it make more sense to go with cut vinyl, than something printed on a clear sticker? In my experience, vinyl holds up pretty well to UV and such, while printed stickers tend to fade. If you go the vinyl route, you could have them made up in a few different colors (white, black and something else... green maybe?) so that everyone can get a sticker that contrasts enough to be easily readable.
Been a little while and there aren't many replies asking for stickers, unfortunately. Perhaps someone could make a Zazzle (or other such website) item or two? That'd address the apparently low volume nature of the demand.
: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another