Welcome syxzys!

I made a little search for signature on CPAN and found two interesting modules: Module::Signature and Test::Signature.
The first one can generate and validate signatures (a manifesto file with md5 sums); the second one is used to validate files during tests. Reading some documentation I discovered that authors of modules can provide signatures file, that will be shown as SIGNATURE link on the module 'homepage' on CPAN.

CPANPLUS uses Module::Signature to check signatures available via CPAN. All of these modules have a SIGNATURE link, but not our beloved Perl :)

Ciao, Valerio

Update: some authors provide CHECKSUMS files in their directory on CPAN.