The knot most closely associated with execution is the hangman's knot, which is also known as the "hangman's noose".
The anatomy of a noose is such as this:
the open end is called a honda
the knots are known as hangmans knots (depending on styles)
the end that is plain is the hitch
In the US, a noose is sometimes left as a message in order to intimidate people. Its meaning is derived from its use in segregation eralynchings. It is illegal to display a noose in a threatening manner in some states such as New York and Connecticut.