There is not a universally accepted or understood meaning to wearing a ring on the thumb. Spiritualists, however, assign each finger a name and a significance, and a thumb ring could indirectly relate to such beliefs.
According to spiritualists, the thumb is the only finger that is not named for a member of the Greek pantheon. The thumb, however, is the central connection of the hand to the brain and controls its movement. Spiritualists also believe the thumb is a direct link to human-will. Therefore, wearing a ring on the thumb could be symbolic of an individual’s personal will, willpower or determination. A thumb ring may also be worn as a symbol of wisdom.