GO responded to my email:
We are pleased to explain what is the meaning about the “GG” logo.
The letter “G” stands for the city “Glashütte”, the home of our manufactory.
The left “G” looks back to our history - more than 170 years watchmaking art – and the
right “G” looks into the present and future.
And we combine these both sides – we now have beautiful and modern mechanical watches with the old and traditional features, like Glashütter stripe finish and perlisage.