To check the GnuPG signature of an RPM file after importing the builder's GnuPG key, use the following command (replace <rpm_file> with the filename of the RPM package):

rpm -K <rpm_file> 

If all goes well, the following message is displayed: rsa sha1 (md5) pgp md5 OK. This means that the signature of the package has been verified, that it is not corrupt, and is therefore safe to install and use.

For more information, including a list of currently-used Fedora Project keys and their fingerprints, refer to http://fedoraproject.org/en/keys.