Q. The question is: what is their significance/origin and why did the Keys
believe they were entitled to bear them?
A. The answers that you seek should be on file with the Office of the Chief Herald of Ireland, especially if the arms were confirmed by Ulster King of Arms some time in the 1930s. I doubt that Ulster would have confirmed the arms without the necessary documentary proofs of paternal pedigree. I suggest that you contact the Chief Herald of Ireland at Dublin Castle. It's a poor blazon and an even poorer emblazonment that has obviously been produced by some heraldic bucket shop. Strangely, I couldn't find any record of the arms in either 'Burke's General Armory, the 'Supplement to Burkes GA' or in Morant's 'General Armory Two'. From where did you obtain the blazon?