The Staffordshire, or Stafford knot, the symbol of the county. It was painted on a  wall in the Beehive pub in Honeywall, Stoke-on-Trent. I had a look at Wikipedia and there is a lot of information there about it. It seems to have a celtic derivation and can be seen in celtic patterns. A noble family in the country town of Stafford used it as their symbol in medieval times. The design is also linked to the Saxon Staffordshire hoard of gold artifacts that was found a few years ago.

It is the simplest knot and this can be multiplied to create various patterns. There is an old stone cross in a churchyard in Stoke-on-Trent which has the symbol carved on it. Incidentally it was used as a surgical knot but was found to be dangerous and would slip if not used correctly.

It was also said to have been used as a knot to hang three men because the hangman could not decide who to hang first. This is not believed to be true and is probably an urban myth.