It appears to be Masonic. The letter "G" figures prominently in Freemasonry. In the lower degrees, the initiate is told that this letter stands for "God" and for "Geometry", which the Supreme Architect of the Universe used to design this wonderful Cosmos. Similar to this:
The reverse of an American gold, diamond and enamel Masonic Scottish Rite, York Rite and Knights Templar watch fob, c.1920; featured is a Maltese cross, crown and sword and the 'In Hoc Signo Vinces'/'In This Sign, Victory' legend of the Knights Templar.