Without the ampersand, I might have suspected Átha Cliath Gas Company, a bi-lingual possibility for early form of Dublin Gas Company. With the ampersand, I am clueless.
And the internet has not provided the answer. Sometimes it is more rewarding when the puzzle beats google and lingers unsolved for a time.
This iron cover was spotted a week back on Monck Place in Phibsboro. Inspiration as to meaning still awaited.