Dubious origin politically, geographically and historically; but a popular flag anyway.
(Unlike the Orange Cross, the Safety Orange Cross is internationally recognised to represent emergency response. It should be distinguished from this more local Orange Cross, which has its roots in Ireland.)
Northern Ireland is part of the United Kingdom and as such, uses the Union Flag.
Until 1974 however, the Government of Northern Ireland used a local flag, known variously as the Northern Ireland Flag, the Ulster Flag or the Red Hand Flag, depending on the speaker's political views. Northern Ireland Flag implies the area is part of Ireland which of course it is, geographically, just as North Korea and South Korea are geographically Korea.
But it also has political overtones for some people, who prefer to call it an Ulster Flag, since this is the name of the province. But geographically, that is not accurate because three of the nine counties are within the southern Republic of Ireland. Politically, the term Ulster avoids using the term Ireland.
Red Hand Flag
On this page we'll stay in the middle and call it the Red Hand Flag.
Union Flag, 1606
St. Patrick's Cross
Red Hand Flag formerly used by the Government of Northern Ireland
They also use the old Government of Northern Ireland's flag which has the English Cross of St. George, a crown to represent the British monarchy, and a red hand within a star.
Orange Cross Flag
In admiration and respect of King William of Orange, they sometimes change the colour of the cross and refer to this flag as the Orange Cross as a contrast to the red saltire of the 'Irish' St. Patrick's Cross.
So much for the colour. As for the red hand, one legend says this comes from one of Ireland's many invasions from England (or Spain, according to another version).
The leader of the raid promised a prize to the first man to touch land with his right hand. All the men raced to the shore and just as they approached, left-handed Hugh O'Neil sliced off his right hand and threw the bloodied member onto the beach, thereby winning (hands-down?) the province and becoming one of the great Irish chieftains.
There are other Celtic legends including the story of two giants engaged in battle; one had his hand chopped off and this left a red imprint on the rocks.
Or it could be from the argument between a couple of Milesian chiefs, who decided to settle their claim over Ireland with a boat race, whereby the first man who put his right hand on the shore would be the ruler. O'Neill chopped off his right hand, threw it ashore. O'Neill and his descendants ruled Ulster until Hugh O'Neill had to surrender to the English in 1603.
For the star image behind the hand, some say this is the Star of David and symbolic of David and the Pharez line of Judah. But more popular is that the six-pointed star represents the six counties of Ulster that make up Northern Ireland.
The crown, either Tudor or Edwardian, symbolizes the union with Britain.
The Red Hand flag ceased to be the official flag of Northern Ireland in 1974 but its copy, the Orange flag, is still widely used by Loyalists and the somewhat less assertive Unionists.