Obverse Mint

Why on the back of AU coins it says IRE?
Look at the picture linked below.
http://4.bp.blogspot.com/_Cgkg7Ju_kac/Slp7ZOhfVwI/AAAAAAAABik/VCfhVA6l4J0/s400/2009-Uncirculated-Coin-Royal-Australian-Mint-$1-obverse.jpg
Just under the Queens neck it says in tiny font “IRE” what does this stand for? what does this mean, i just noticed it today and it’s driving me NUTS
I have just been checking some coins with a magnifying glass it is actually IRB on the five coins that I checked , but older pre 2001 coins have nothing there , at least not any of mine. But I don’t know what it is , maybe some kind of mint ID ?
Just by the way the Queen is on the front of the coin not the back.
5 rm coin, 1935, with mint error: turned reverse