Red Hand is the symbol of "Ulster," most correctly. The ancient Irish province of Ulster includes three Irish counties which are NOT in Northern Ireland. One of those counties - Monaghan - has the red Hand in its crest.
The Red Hand is represented in the flag of Northern Ireland.
It is included in the county crests of several Ulster counties, inside and outside Northern Ireland.
In recent years it has featured most notably on jersey of Tyrone when they twice won the All Ireland Gaelic Football senior championship (Cup), which is played for among all the 32 counties in Ireland, plus London and New York.