Nice-looking button.
That looks like an Imperial crown, so I don't believe it to be Irish. think you should be looking at continental Europe, and probably Prussian Empire. That style of crown is and was also used pretentiously on blazer buttons from elsewhere. I can't make out what the three 'columns' are in the heart, but if it's a serifed 'III' it could conceivably be for Friedrich Wilhelm III, who ruled Prussia until 1840. However, it's not the usual Cypher used for him. I don't think it's military, but it might be 'official' in some other sense.