The seal of the United States Department of the Treasury.
The original seal dates from the Board of Treasury during the Articles of Confederation, and so predates the department (and Federal Government) itself.  The current design is a slight simplification of the original, introduced in 1968.
The seal's arms depicts balancing scales (to represent justice), a key (the emblem of official authority) and a chevron with thirteen stars (to represent the original states).

For more information, see here.
Extracted from PDF file here.
U.S. Government.  The original 1780s seal is believed to have been designed by Francis Hopkinson.