How a Claddagh ring is worn on the hand tells the wearer's romantic availability.
If the ring is on the right hand with the heart facing outward, the person is not in any serious relationship,"their heart is open".
When worn on the right hand with the heart facing inward, the person is in a relationship, "someone has captured their heart".
A Claddagh worn on the left hand ring finger, facing outward away from the body, indicates that the wearer is engaged. 
When the ring is on the left hand ring finger and facing inward, it means that the person is married.