I noticed that the postgis23_96-2.3.3-1 RPM is not signed. It is strange that it was updated on 7/24/2017 since it is an older version.

This is the URL I got the RPM from: https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64

And this is the exact package.

postgis23_96-2.3.3-1.rhel7.x86_64.rpm 2017-Jul-24 08:25:04 4.1M application/x-redhat-package-manager

Regards,
Jeff Hastings