Check CPAN, there are good signature modules. (No links; they have been posted often, I write on an iPad while eating pizza without fork/knife.)

Edit: After pizza, clean hands. :-) Just google "cpan method signatures" or similar. The extensible syntax of Perl is really cool. Here is a Moose specific example with type constraints: http://search.cpan.org/~ether/MooseX-Method-Signatures-0.47/...