Seal of the United States Treasury Inspector General for Tax Administration, a bureau of the Department of the Treasury which provides oversight to the IRS.  The design is the same as the Treasury seal with a TIGTA inscription.
Extracted from PDF version of the March 1999 Semiannual Report (direct PDF URL [1]), with colors slightly changed to match the icon on the http://www.treas.gov/tigta/ homepage.
U.S. Government