The winning design was drawn up by a high school junior from the North Side.
St. Gregory junior Suthida Lestpanichphan got the honor.
The theme for this year's sticker design was "Education is key."
More than 400 students representing 50 schools took part.
Suthida's hand-drawn image got the nod. She gets a $1,000 saving certificate for her efforts.
"I want to say thank you to everyone who supported me," said Suthida. "It's such an honor to get to come here today, so thank you."
The winning design will be displayed on more than 1.2 million vehicles, effective June 30 through June of 2012.