My thought is that instead of the ring having significance to membership in an outside group such as Masons, the GB may have had rings designed and made for themselves and their 'helpers'. Possessing such a ring could then identify the wearer as a member of the exclusive JW leadership. Since JWs are so fixated on position, differences in color or design could then denote rank or position.
I expect that even if true, anyone in the know would never verify. Just as elders possess their manual which at least earlier on, they were instructed to deny the existence of and not show to anyone, membership rings could more easily be kept a secret since there are so few that would possess one and copies could not be easily made.