license for public domain software?

[Jeremy Lavergne]

> What should the 'license' be for software that is in the public domain? I am updating py-novas_py; the license says:
> 
> This software was produced by the United States Naval Observatory at the expense of United States taxpayers, and is therefore not suseptible to copyright, because a copyright would place taxpayer property under private ownership. Since it is not copyrighted, it cannot be licensed; it is simply free.

I'd go with Permissive unless a better option appears our source code:
http://trac.macports.org/browser/trunk/base/portmgr/jobs/port_binary_distributable.tcl