A gruesome garrote?
If you’ve seen the Godfather, you know exactly what a garrote wire is and hot to use it. The OP found a string with ring handles on either end while out in the woods. Maybe they found an incriminating piece of a past crime that the bad guy tossed into the wild.
However, this wasn’t the case. One commenter let the OP know that this rope-ling apparatus is a wire saw. It’s a kind of portable saw that lumberjacks use to saw down thin trees or branches.