The US Postal Service's 'Go Green' sheet of stamps are drawn by an animator, Eli Noyes. Animated versions of the stamps are online as are his preliminary sketches. This appears to be a main page of information, and here's the press release.
The USA Philatelic cataloge (16: 2, 2011) explains the stamps design:
"The idea was to keep it light," says art director Derry Noyes, "not to scold as if shaking a finger and saying, 'Go do all these things and make the planet better."
She knew of one artist who might be perfect for the job: a filmaker and animator who founded a nonprofit group, Climate Cartoons, to create kid-friendly environmental messages. So in the spirit of "reuse and recyle," Derry recyled one of her oldest relationships - recruiting her older brother, Eli, for the project.