Esoterically the practice of wearing a thumb ring means you’re either trying to emphasis your independence and individuality or inhibiting some aspect of the self. I guess its whatever you feel like or you may be doing both.
Historically, (ie, the 1500’s) wearing a thumb ring meant you were a doctor or pretending to be one. Also, centuries ago women would wear their husbands wedding rings on their thumbs when they left for battle or died.
You can also choose which thumb to wear a thumb ring on. To wear a ring on the left hand is a reflection on the subconscious or your instincts, beliefs, and basic attitudes. To wear a ring on the right is a focus on the conscious, reflecting logic, awareness, and the material world. More recently to wear a thumb ring on the right indicates that you are into same sex relations.
Many people seem to be concerned about whether or not its okay for them to wear a thumb ring. I say forget the current trend in meaning and wear one if you want because it constantly changes. Interestingly thumb rings are usually interchangeable with your index or middle finger. They are also more comfortable when worn on the non-dominant hand.
Currently thumb rings are sold everywhere from gumball machines to upscale jewelry manufacturers. They can be made of plastic or platinum and made in a simple band or elaborate framing with braiding, or shapes like hearts inside.