English: The former flag of the Executive Committee of the Privy Council of Northern Ireland, from 1953-1972. This flag has had no official status since 1972 and is widely regarded as the emblem of one community only. It should not be used to represent present day Northern Ireland geographically or as a political entity.
Español: Bandera usada por el gobierno de Irlanda del Norte de 1923-1972. Actualmente de uso no oficial.
Source
It is from the xrmap flag collection, specifically "uk_north_ireland.svg" in flags-2.6-src.tar.bz2.
The README file in that collection says of the SVG flags "We release them in the public domain".
Licensing
Public domainPublic domainfalsefalse
This work has been released into the public domain by its author, Jean-Pierre Demailly. This applies worldwide. In some countries this may not be legally possible; if so: Jean-Pierre Demailly grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.