A normal hardware-store snap hook forms the heart of the Bill Varnedoe's V-knot (a.k.a. Varnedoe Grip Knot). This is yet another semi-mechanical version of the Helical Knot. The open end of the snap link should be on top, since otherwise it tends to open when the knot is raised. Even when properly oriented, the knot is not particularly secure or strong, and I recommend avoiding it.
Snap hooks are not strong enough to be safe.