The Olive branch has long been a symbol of peace. Incorporated into the Great Seal of the United States is an eagle holding an Olive branch in its right talon. The seal was designed shortly after the United States declared its independence from England in 1776. The seal symbolizes both power and peace. The basic design of the seal has been incorporated into the seal of the President (with a few modifications), the seal of the Supreme Court, the seal of the Senate and many more.
Olive branches are also common on coins.
The lady "Liberty" is found on many coins and in some of them she is holding an Olive branch. The image above is the "Standing Liberty Quarter".
The Kennedy Half Dollar has the Seal of the President on its reverse side with the eagle holding the Olive branch.
Department of Defense seal is similar to the commemoration seal above. " Below the eagle a wreath of laurel to dexter and olive to sinister...The laurel stands for honors received in combat defending the peace represented by the olive branch" ( in Latin sinister means 'on the left side' and dexter means 'on the right side'.)
The three tree species that are very common on United States seals and coins are the Olive, the Laurel and the Oak.