The nearest look out post to the Blasket Islands is Dunmore Head which is on the mainland. It was LOP number 38. There wasn’t a LOP on the Great Blasket that I was aware of and most signs were linked with the nearest LOP hence the classification. At the moment, it does not look to me as though the number is intact for this location so I cannot confirm absolutely.
Location on Google is clouded over.
If you look carefully at the base of the tower, you can just see the remains of the R and the E at the end of EIRE.
There is actually an historic aerial photograph of this sign too which the Military Archives have published on their social media/Flickr stream
Updated August 2018
This seems to be a better candidate: Map is updated accordingly
LOP Mizen Head, Cork
You can barely see the remaining stones of the EIRE sign here in the centre of the picture. Only the I remains really visible