This is a great question for us to answer! Our club was on the forefront of the Black Ring movement back in 2013, when we hosted the very first Black Ring party with the support of the popular swingers website, Kasidie.
Wearing the Black Ring on your right hand signifies that you are in the “swing” or Alternative Lifestyle This allows others to spot fellow lifestylers.
We’ll usually wear them when we are out as a couple or with other swingers; so it’s not a coincidence that we are all wearing black rings on the same hand. This makes it easier for other lifestylers to spot us in the crowd, especially at public swinger meet and greets. It is also a great way to spot a 'hot date' you're meeting for the first time.
There is no specific finger to wear it on, though it is most popular to wear it on the ring finger or the pinky. My Wife wears hers on her ring finger as i prefer my pinky finger.
As you can see from the photo below, taken at one of our events, it’s a matter of preference.
Image source Deviate Network Black Ring Party March 8th 2013
That being said; some people who wear the black ring on the middle finger signifies they are asexual, not necessarily a 'swinger'.
We wear our black rings nearly everyday and encourage our members in the lifestyle to do the same.