USIS - United States Information Service, the overseas name for the (now-defunct) United States Information Agency.
United States Immigration Service, a name sometimes used in the past, possibly both formally and informally at different times, to refer to at least one of the many U.S. federal agencies of the executive branch which have implemented U.S. immigration law. (Today the principal such agency is the U.S. Immigration and Customs Enforcement).
This metal cover was used to cover your regular button while you were attached or working for the USIS. It is completely removable.