WASHINGTON-Aircraft nose art with the words "Let's roll!" -- America's two-word marching order in the fight against terrorism will be displayed on various aircraft throughout the Air Force as a way  of recognizing the heroes and victims of the Sept. 11 attacks on the United States.  The words were made famous by Todd Beamer, a passenger on Flight 93.  Beamer, a 32-year-old businessman, Sunday school teacher, husband, father and hero, led other passengers in fighting terrorists for control of Flight 93 before it crashed into a field in western Pennsylvania. He was overheard on a cellular phone reciting the Lord's Prayer and saying "Let's roll!" as passengers charged the terrorists.  "'Let's roll!' has served as a rallying cry for this nation as we go forward in our war on terrorism," said Air Force Chief of Staff Gen. John P. Jumper. "We are proud to display this new nose art on our aircraft."  The passengers of Flight 93 won one of the first victories in the fight against terrorism. There has been much speculation about the terrorists' intentions for Flight 93, but it is widely believed that either the White House or the U.S. Capitol building was the intended target.   The nose art design depicts an eagle soaring in front of the U.S. flag, with the words "Spirit of 9-11" on the top and "Let's roll!" on the bottom. The design was created by Senior Airman Duane White, a journeyman from Air Combat Command's multimedia center at Langley Air Force Base, Va.  The Thunderbirds and other Air Force demonstration teams will apply this nose art on all aircraft, while major commands and wings will be authorized to apply the nose art to one aircraft of their choice.   For thousands of years, warriors, such as the vikings, Zulus, Native Americans, samurai and many others, have followed a tradition of decorating their instruments of war. These instruments could include the warriors or their weapons. The Air Force has used nose art throughout much of its history, and for a variety of reasons.   The "Let's roll!" nose art is being used to continue the remembrance of the events of Sept. 11, spur on the nation's current patriotic spirit and pay tribute to the heroes and victims in the war against terrorism.   It is anticipated that the art will start to appear on Air Force aircraft around Jan. 15.