Security Thread and Microprinting

1990

A security thread and microprinting are introduced in Federal Reserve notes to deter counterfeiting by copiers and printers. The features first appear in Series 1990 $100 notes. By Series 1993, the features appeared on all denominations except $1 and $2 notes.

United States Notes Discontinued

1971

Because United States notes no longer served any function not already adequately met by Federal Reserve notes, their issuance was discontinued and, beginning in 1971, no new United States notes were placed into circulation.