This is a really cool guerrilla promotion that was thought up by Brave advertising agency in Sydney, Australia, for an environmentally-friendly construction company named Boral. In order to promote their eco-friendly cement trucks, the agitators on them were covered in promotional stickers that displayed vibrant, hippie-esque colors along with the slogan "happily powered by natural gas."
I am extremely impressed with the ingenuity on this campaign. The execution is flawlessly tied in to the environmentalism which it addresses, not to mention the creative use of a space I've rarely seen used for advertising before. The only thing they should clarify is what impact cement trucks that do not run on natural gas have on the ecosystem, but I understand that this is difficult to do on the cement trucks themselves. Their website actually contains information regarding the environmental impact, but perhaps some traditional advertising in the local area would reinforce the significance of their environmental initiatives. Perhaps even a tease to their website would have been sufficient.
All I've got to say is: bravo! I wish there were more guerrilla promotions out there like this one! But then I suppose they wouldn't be as effective...