Over 700 Malicious Typosquatted Libraries Found On RubyGems Repository.
https://thehackernews.com/2020/04/rubygem-typosquatting-malware.html
Topic of signed gems seems to have been last raised in... 2013 https://github.com/rubygems-trust
#python packages could have PGP signatures like forever (twine --sign), but predictably nobody uses it.
There's an active discussion on PEP 458 to sign packages at pypi (centrally) https://discuss.python.org/t/pep-458-secure-pypi-downloads-with-package-signing/2648/123