(Bloomberg) -- Treasury Secretary Janet Yellen, whose signature will soon appear on US currency, joked with talk show host Stephen Colbert that she worked hard to avoid the ridicule faced by some of her recent predecessors over their sloppy handwriting.

“Tim Geithner and Jack Lew signed the currency and their signatures were so illegible that people made fun of them,” Yellen said Wednesday during a taping of “The Late Show with Stephen Colbert” on CBS. 

“Secretary Lew, he signed it with something that looked like eight circles that were connected,” she said with a laugh. “So, I knew this was something you could really screw up, and I wanted to get it right, and I practiced and I practiced.”

The Treasury chief is scheduled to visit a Bureau of Engraving and Printing facility in Fort Worth, Texas, on Dec. 8 where she’ll unveil the first dollars bearing her signature.

The notes, which will enter circulation in January, will be the first signed by a female Treasury secretary. They’ll also be signed by Lynn Malerba, the first Native American woman to serve as US treasurer.

Yellen, a former US Federal Reserve chair, also responded gamely to Colbert’s questions about secrecy at the central bank. 

She burst out laughing when he said, “There’s lots of conspiracy theories that the Fed is a cabal and you guys wear robes and sacrifice a goat.” 

Yellen ignored the reference to goats, but conceded that decades ago the Fed shrouded its policy decisions in mystery.

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