If I'm not mistaken the latest available rpms for Red Hat 7.3 is missing the signature, doing a simple
$ > Name : postgresql93-server
$ > Version : 9.3.20
$ > Release : 3PGDG.rhel7
$ > Architecture: x86_64
$ > Install Date: (not installed)
$ > Group : Applications/Databases
$ > Size : 16551335
$ > License : PostgreSQL
$ > Signature : (none)
$ > Source RPM : postgresql93-9.3.20-3PGDG.rhel7.src.rpm
$ > Build Date : tor 7 dec 2017 22:41:49
$ > Build Host : koji-rhel7-x86-64-pgbuild
$ > Relocations : (not relocatable)
$ > Summary : The programs needed to create and run a PostgreSQL server
$ > Description :
$ > PostgreSQL is an advanced Object-Relational database management system (DBMS).
$ > The postgresql93-server package contains the programs needed to create
$ > and run a PostgreSQL server, which will in turn allow you to create
$ > and maintain PostgreSQL databases.
Doing the same command on previous rpm's reveals a the signature "DSA/SHA1, ons 8 nov 2017 21:52:18, Key ID 1f16d2e1442df0f8"