These ÉIRE markings were set-up around various locations on the Irish coast during World War 2. Éire is the name of the country in the Irish language. In total there were 82. They were designed to indicate to overflying aircraft from all sides that they were flying over a neutral country.
Despite their neutrality, the Irish government did not detain any Allied airman that were forced to land on their territory. They were also privy to the numbers, which helped with navigation.