The ring Sean gives his mother for her birthday is a Claddagh ring, a traditional Irish ring which represents love, loyalty, and friendship.
The three main characters all hail from Ireland and Scotland. Kerry Condon and Robert Sheehan are Irish while David Tennant is Scottish. Kerry Condon and David Tennant have an American accent for the film.
DCcomics has a character called the Bad Samaritan, a man in black with black sunglasses who works as an enemy agent.