The Happy Ring House (or McDowell's Jewellers to give it its proper title) is located at No. 3 Upper O'Connell Street. Built in 1917, it reputedly houses girders which were salvaged from the GPO after its destruction the previous year. McDowell's had been established in 1870, and the fourth generation of jewellers still operate from this building.
Naturally the most notable feature of the building is the huge neon sign on the frontage. It dates from 1952 and is one of the few surviving such signs from that era. The building (including the sign) is now a protected structure.
Many regard the neon as tacky, and they're absolutely right - but I love it regardless. It evokes an image of a busy O'Connell Street in its mid-twentieth century prime, with trams gliding by, bells ringing, and throngs of snazzily-dressed people visiting the street's cinemas and restaurants. As well as that, like many Dubliners, my parents bought their engagement and wedding rings here!
I really recommend the blog Project Neon! for anyone interested in this type of classic neon signage.