I don't know.
The Treasurer of the United States
Since a Fed employee doesn't work for the Treasury, I'm not sure why you think the Treasurer would sign. Are other government checks signed by the Treasurer?
BTW the old joke about the Federal Reserve is that they were not listed in the (blue) government pages of the phone book.
And yet they have a .gov URL and the President appoints their chairman.
Any other "private" corporations get their chairman appointed by the President and approved by the Senate?