That's funny! A funny way to express the Northern Ireland's historical anger towards UK...Sock-on-the-nose postmark...But the stamps are issued by Royal Mail, from England/UK. Northern Ireland does not have postal autonomy in issuing stamps, right?:D
You're right! NI hasn't the right to issue own stamps. The postmarks are indeed placed on a funny way, directly at the Queen's face.There are definatives for Northern Ireland and a miniature sheet where issued last year too.