The concept is the shape of a prancing "Gnu" as a guardian.
The text of "GnuPG" with red shield on the "PG" part of the text. The red shield represents GnuPG as security application.
The sketch of "Gnu". Giving an image of great strong guardian just like GnuPG.
This is my next design for GNUPG. The concept is a keylock constructed from "GNUPG" text. I've made a slight variation here. One with one uniform color and one with white color on the "PG" text.