Foul (nautical)

Foul is a nautical term meaning to entangle or entwine, and more generally that something is wrong or difficult.

It is usually applied to the state of an anchor, which has become hooked on some impediment on the seafloor, or has its cable wound round the stock or flukes.

The term is generally utilized when speaking of items of historical value such as the US Navy chief petty officer emblem.

[1] The foul anchor is also the official seal of the Lord High Admiral of the United Kingdom.

Ships would display a foul anchor to indicate to officers on shore that sick persons were on board, prompting further investigation and possible quarantine.