Guinness uses the harp of Brian Boru, or Trinity College Harp as their trademark. This circa 14th century harp which is still visible at Trinity College, Dublin has been used as a symbol of Ireland since the 16th century. Guinness adopted the harp as a logo, however it is shown in a form that faces left instead of right as in the coat of arms.

Photo: Guinness Brewery, St James Gate, Dublin, Ian C. Whitworth Photography