Reef knot aka square knot, is a well known knots among scouts.
I came across this interesting display at the Comlara Park situated in Illinois.
To support this picture I wanted to share, I took help of Wiki and found some interesting stuff about this simple "Knot".
A reef knot is formed by tying a left-handed overhand knot and then a right-handed overhand knot, or vice versa. A common mnemonic for this procedure is "right over left; left over right", which is often appended with the rhyming suffix "... makes a knot both tidy and tight".
The reef knot is at least between 4,000 and 9,000 years old.
The name "reef knot" originates from its common use to reef sails, that is to tie part of the sail down to decrease its effective surface area in strong winds.
Other uses of this simple knot can be traced to medicine in tying bandages.....known to the ancient Greeks as Hercules knot.
Used since ancient times to tie belts and sashes, a modern use in this manner includes tying the obi (or belt) of a martial arts keikogi.
A note of caution however that it is an insecure knot, unstable when jiggled, and is not suitable for supporting weight.