perl-Module-Signature-0.81-2.fc27 build- and run-requires gnupg package. I propose to move from gnupg to gnugp2 package. gnupg2 is actively developed, gnupg2 has different public key database from gnupg, gnupg2 is in Fedora's minimal build root. Module-Signature-0.81 code checks for gpg2 executable too, thus I guess it can work with it. Though I did not test it.
perl-Module-Signature-0.81-3.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-141e1b40a6
perl-Module-Signature-0.81-3.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-141e1b40a6
perl-Module-Signature-0.81-3.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.