Recently a happily married couple came to have the pattern on their wedding rings made into permanent symbols of their devotion. His arm band matches her anklet, both replicating an ancient nautical knot that is a favorite used to form a decorative loop at the end of a lanyard. It is variously known as the double diamond, Carrick bend, and Josephine knot. In heraldry it is the Wake knot, and figures on the badges of many families.
Their rings were crafted by the esteemed jeweler Wilfy Mac Manus, of Mac Manus & Sons, who I recommend unhesitatingly for Celtic jewelry.