Made in Ireland Claddagh ring

I was given this ring 22 years ago, by a family member who bought it at a flea market for $20.00. In my new interest of the show "pawn Stars" I got curious if the markings in the ring meant anything. On the inside it says Made in Ireland just behind the heart and on the band it has the letters O and C stamped on it/ in it. (It's hard for me to tell if there is a U between those two letters or just the space between them) Then next to that in little boxes I believe the letters are H G R but then again, it's hard for me to make out. Do these marks have any special meaning? are they common. Any answers would be great!