Omar Sarhan writes:

An interesting symbol outside the church of St. Agatha near the 5 lamps in Dublin.
ن (the Arabic letter for “N”) is used in ISIL controlled parts of Iraq/Syria. Christian property is marked with an “N”, or ن , it is the first letter of the Arabic word for Christian, “Nasrani” or “Nazarene”. It has being documented that property is often seized after some time. In many western countries the symbol is used to show solidarity with Iraqi Christians.