The "Three Crowns" are the official Coat of Arms of Hull City Council but are now widely recognised as the emblem of the City of Kingston upon Hull.
The coat of arms is described ("blazoned") in the official language of heraldry as "Azure, three ducal coronets in Pale Or" - on a blue background, three gold coronets or crowns arranged vertically.
The Three Crowns have been used as the City's Coat of Arms since the early 1400s. They appear on the Mayor's seal as early as 1415. A depiction of the shield in stained glass in St Mary's Church, Lowgate, dates from the reign of King Richard III (1483-85).
The College of Arms, the official body which regulates heraldry in England, confirmed Hull's right to use this Coat of Arms in the 1600s. Since then, virtually every public building in the City has been decorated with the Three Crowns.
As to whether they are Crowns or Coronets, it's clear that they started out as royal crowns, but the language of heraldry has evolved, and their official designation is "ducal coronets." But it scarcely matters that we all know them as the Three Crowns.
One theory is that they represent the Three Kings of the Christmas story who travelled from the East to bring gifts to the Baby Jesus, just as merchants travelled to Hull from a different part of the East bringing timber and goods from the Baltic. The shrine of the Three Kings is at Cologne, and Hull had trading connections with Cologne and the Rhineland in the Middle Ages.
Another explanation is that the Three Crowns represent the Holy Trinity. In the Middle Ages, the Holy Trinity - the union of God the Father, Son and Holy Spirit - was a popular religious cult in Hull, and Holy Trinity Church (now Hull Minster) and Trinity House commemorate this.
Alternatively the use of three royal crowns is to mark that Hull is the King’s Town, as in Kingston upon Hull, so designated when it was founded by King Edward I in 1299.
It's probable that all of these explanations played a part in medieval Hull people choosing the Three Crowns as Hull's Coat of Arms, and just as likely that it was because they look good!
Hull is unique in being the only city in England to protect its Coat of Arms with an Act of Parliament. Any organization, business or society which wants to use the Three Crowns as part of its brand or emblem has to ask for permission from Hull City Council.
C TMD/1 - Certified copy of the arms of the Hull Corporation as allowed at the visitation of Yorkshire in the years 1612 and 1665/6 signed by George Harrison, Windsor Herald and registrar. Feb 1951.
C BRC - Letters patent granting an armorial badge to Kingston upon Hull City Council, 2004
C BRC - Letters patent granting a coat of arms to the Admiral of the Humber, 2005
City and County of Kingston upon Hull coat of arms, Hull Corporation Development Committee, 1969 [classmark L 929.8]
The Arms of the Town of Kingston upon Hull, T Tindall Wildridge, 1887 [classmark L 929.8]
The Correct Arms of Kingston upon Hull, Thomas Sheppard, 1913 [classmark L 929.8]
The Armorial Bearings of Kingston upon Hull, Joseph Hirst, 1916 [classmark L 929.8]
Download the Kingston upon Hull Act 1984 as a PDF from Legislation.gov.uk.