It's a little odd to me that they left the ring. They stripped him down to his underwear. The ring would have been worth good money in Mexico. Maybe the ring was dropped by one of the killers? The date could be in the format of November 2nd, 1989.
I have thought about 11/2/1989 as well. Perhaps it was an engagement band and this person was to be married. Or vows renewed. Or a "mail order" bride scenario where he ended up getting hustled and killed. Wearing just underwear could suggest he was caught very unaware with a partner. There are lots of confidence and romance scams going back centuries. Ransom isn't always an option. Is there is another victim we aren't aware of? Was this the honeymoon?
That is strange. And why was it off his finger?
Mark Kilroy was a victim during this time of a cult killing. I dont know much about ritualistic killing, but could the ring have been left as an "offering" for some "outcome"? Love magic? Taking clothing but leaving a ring seems odd. There's money in a ring.
I wish we had pictures of the ring and victim, or even the brand of underwear, it would be so helpful.