G = Guadalajara
G = First initial of first or last name
26 = Registration number (maker)
AG = Argentum chemical symbol for silver
Stones are semi precious and/or cut glass.
Date: Possibly mid 1930's to mid 1940's (.925 purity, & is not the .900 of 1900-1920's, with no eagle symbol, and with no 'sterling').
Some suggest as being early tourist trade pieces.