I don't think it's neccessary to include any extra fields for license (nothing stops users from including comments/pod about license), but if one gets included, the license field should state "unknown" by default. There are a lot of posts in the catacombs already, and presenting them as being under any kind of license other than as stated in the code/documentation is just wrong. And finally, if there ever is a license field, perlmonks should have the same disclaimer as the module list (http://search.cpan.org/dlsip?MpdOp):

DISCLAIMER: The status of the Public License field is there for informational purpose only and does not constitute a legal binding of any kind. To obtain proper information about the Licencing terms of a module and its accompanying files, please refer to the distribution of the modules or contact the author as appropriate. Please inform ... modules@perl.org if you encounter any mismatch between the contents of the Public License field and what the distribution actually says about it.

update: Actually, perlmonks ought to have some kind of disclaimer already.