The Truth:  
Obama has used several different airplanes during his campaign but towards the end of his 2008 Presidential run he was flying aboard a Boeing 757 chartered from North American Airlines.  This eRumor resurfaced once again while he was running for his second term and some version say that the official jet of the President of the United States, Air Force One, had been converted with his campaign logo.  That is fiction.

Until mid-July of 2008, the airplane had the markings of the North American Airline fleet, which included an American flag on the tail, which is a part of the paint scheme for the airline.  The senator's plane was completely repainted, however, to reflect Obama's campaign (as is frequently the case in presidential races).  The picture circulated with the eRumor shows the new paint job.  The American flag of North American Airlines is replaced with Obama's "O" campaign logo.

There was a small American flag on each side of the airplane and toward the rear near the airplane's FAA registration number.