"P. O'Neill"
The IRA traditionally uses a well-known signature in its public statements, which are all issued under the pseudonym of "P. O'Neill" of the "Irish Republican Publicity Bureau, Dublin". According to Ruairí Ó Brádaigh, it was Seán Mac Stiofáin, as chief of staff of the IRA, who invented the name. However, under his usage, the name was written and pronounced according to Irish orthography and pronunciation as "P. Ó Néill". According to Danny Morrison, the pseudonym "S. O'Neill" was used during the 1940s.
Read more about this topic: Provisional Irish Republican Army