It is not a typo.
The new $100 bill, which entered circulation last week, bears the signature of former Secretary Timothy Geithner on purpose.
Geithner stepped down from the Treasury early this year, but the new design -- which includes an image of a bell that disappears into an inkwell, and a 3-D ribbon down the front --was approved during his tenure. It is called the Series 2009A, for the year he OK'd the design.
Geithners signature wont be there for long, though. The next batch will bear the signature of Jacob Lew, who became the secretary in February of this year. The series is updated when there are significant changes, like the naming of a new Treasury chief.
A spokeswoman for Bureau of Engraving and Printing said it is unclear when the next batch, which will be called Series 2013, would be printed. New plates have to be created for the printing.
Lews signature has been a point of ridicule. In January, President Obama joked that he considered rescinding Lew's nomination after seeing it. Lew has apparently been working on it. In June the Treasury released a copy of Lews signature that would appear on the new currency.
It is still tough to read, but it now looks more like a signature and less like the squiggly lines we all draw when dealing with a stubborn pen.