Alan Gardner broke the story, but here's the citation from the Robert F. Kennedy Memorial's press release:
Cartoon Winner: Signe Wilkinson’s editorial cartoons from The Daily News were instrumental in moving the issue of violence in disadvantaged neighborhoods and schools to the top of the city’s agenda. Her cartoons offer a “steady drumbeat of funny, moving and shocking images”. The RFK Cartoon Judges write, “Her series attacking gun violence in Philadelphia spared no one and drew complaints from everyone- the hallmark of any good cartoonist”.
Some DC-area cartoonists are usually on the awards panel - perhaps they'll chime in.
Also note, "All recipients of the 40th Annual Robert F. Kennedy Journalism Awards will be honored at a ceremony on Tuesday, May 27, 2008 at 6:30 PM at the Newseum in Washington, DC."