According to Irish author Colin Murphy, a Claddagh ring is traditionally worn with the intention of conveying the wearer's relationship status:
On the right hand with the point of the heart toward the fingertips: the wearer is single and might be looking for love.
On the right hand with the point of the heart toward the wrist: the wearer is in a relationship; someone "has captured their heart"
On the left ring finger with the point of the heart toward the fingertips: the wearer is engaged.
On the left ring finger with the point of the heart toward the wrist: the wearer is married