It's a half hitch on a half hitch, creating a double slip knot that stops on itself. Each end is half hitched around the other, so that they overlap in between. Not a bad way to secure something; if you make the two knots real tight, you can draw up the slack and they will take a good bight that will keep the whistle, or whatever you are tying off, pretty snug up against the anchoring piece. They are easy to untie as well.