After reading some recent stuff about CPANTS, I have decided to include a META.yml and a SIGNATURE file in my CPAN modules. I am looking for guidance from the monastery on the best way to go about this.

The current versions of Module::Build and ExtUtils::MakeMaker will generate a META.yml file for you automatically when you create a distribution. Personally I wouldn't yet worry about any of the features in the META spec that aren't automatically generated.

For SIGNATURE files use Module::Signature as you've already discovered. If you're using Module::Build you can automate the signature generation with the sign argument.