A. The service sword knot is braided of black leather or approved
synthetic material, with a simulated large knot,
two sliding keepers, and a hook and eye closure. 
The sword knot will be attached to the sword at all times.

    B. The knot is attached to the sword by passing the small end
through the eye in the pommel and securing it to the hook
above the large end of the knot. One keeper will be drawn taut
immediately below the pommel; the other immediately
above the large end of the knot.  Both strands of the knot
are then looped in a clove hitch over the rear hilt at the cross guard,
next to the acorn, and drawn taut so that the large end of the knot hangs
free and does not fall below the upper brass rings of the scabbard. 
The clove hitch "crossover" is worn inboard.
From the USMC Uniform Board (PMCUB)