As of today, January 28, 2020, I am the official owner of the trade mark capo-ble banjo®. This link will take you to the announcement:
What that means is that you can’t use that trade mark without my permission. You’re welcome to use the term capo-ble banjo, just not the trade mark with the “®”.
If you’re a banjo maker, and want (non-exclusive) rights to the trade mark, no problem. I will license it to you for $1, on the condition that you contract to use it only for 5-string banjos with all 5 strings the same length.