GoldGold Ring with GOLD HALLMARKS found Metal Detecting by: Anonymous
The ring is Italian. ca. 1968 - present. "554" is the number of the smith. Each smith registered during this period in Italy was assigned a number. The letters "AR" are the abbreviation for the Italian provence - ARREZZO.
As you correctly mention,the standard mark,"750" is the millesimal value for 18ct gold. This is the minimum gold standard for sale in Italy.