From the character's tenth solo press conference (28 Oct 2003):
Q: Mr. President, if I may take you back to May 1st when you stood on the USS Lincoln under a huge banner that said, "Mission Accomplished." At that time you declared major combat operations were over, but since that time there have been over 1,000 wounded, many of them amputees who are recovering at Walter Reed, 217 killed in action since that date. Will you acknowledge now that you were premature in making those remarks?
THE PRESIDENT: Nora, I think you ought to look at my speech. I said, Iraq is a dangerous place and we've still got hard work to do, there's still more to be done. And we had just come off a very successful military operation. I was there to thank the troops.
The "Mission Accomplished" sign, of course, was put up by the members of the USS Abraham Lincoln, saying that their mission was accomplished. I know it was attributed some how to some ingenious advance man from my staff -- they weren't that ingenious, by the way. But my statement was a clear statement, basically recognizing that this phase of the war for Iraq was over and there was a lot of dangerous work. And it's proved to be right, it is dangerous in Iraq. It's dangerous in Iraq because there are people who can't stand the thought of a free and peaceful Iraq. [...blah blah etc].
From the Telegraph 30 Oct 2003:
However, Mr Bush's spokesman, Scott McClellan, later conceded that the banner was actually made and supplied by the White House.
"We took care of the production of it," he said. "We have people to do those things. But the navy actually put it up."