Over time, the Treasury and the Fed had become resistant to changes in the currency, feeling that public familiarity with long-established designs was an effective deterrent to counterfeiting. Nevertheless, as technology advanced and counterfeiters became better able to imitate the BEP's genuine article, it became increasingly clear that new, advanced security features would have to be added to the nation's paper money.
The new enhanced currency, dated Series 1990, went into production in 1991, beginning with the $100 denomination. Although it had, at first glance, the same designs as the previous series, two new features had been added. One, a polymer strip embedded in the paper itself, was designed to be visible only when a note was held up to a light source; the strip was printed with the letters "USA" and the denomination (in figures on the $100 and $50, but spelled out on the smaller denominations) repeated along its length, alternately inverted, and was positioned vertically in each note, just to the left of the Fed seal. The other new feature, a row of tiny microprinting around the frame of the central portrait on each note, could be read clearly only under magnification; the words "The United States of America" were repeated several times on each side of the portrait. Neither of these security features could be easily reproduced by low-tech counterfeiters using color copiers or similar widely available equipment. By 1994, all denominations down to the $5 had been produced with the new security features; the $2 and $1, not often targets of counterfeiting, were left unchanged.
Even these enhancements, however, left our currency substantially less advanced than that used by many other nations during the same period. Finally, in 1995, official resistance to change was overcome, and U.S. currency underwent its first complete, systematic overhaul since the introduction of the small-size notes almost seventy years before.
Next: The Series 1996 redesign