This is the package signature as generated by The GnuPG. This signature identifies the party that created the package. By verifying it you are sure that the package coming from a trustworty person or organization.
Here is the package signature:
-----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (GNU/Linux) iD8DBQBH4K/tqesEzEdeXBERAp8SAJ9WODGyVqHrFWJvQ+OelvP0AzjEowCfVGwO sxJROpSJWRO6TcmrNmiw7gA= =LC9q -----END PGP SIGNATURE-----
You can save this signature in a text file (e.g. graphviz-2.18-i486-1gds.tgz.asc) in the same directory where the package file (graphviz-2.18-i486-1gds.tgz) resides and you can verify it by issuing the following command:
gpg --verify graphviz-2.18-i486-1gds.tgz.asc
NOTE: You need to import the public key of SlackPack first:
gpg --import KEY