Not quite.
"san" is used for foreign saints (San Nioclás) and especially apostles.
The use of "Naomh" for saint is a new usage.
It used to be, for example, either the name on it's own Pádraig or Colm Cille - everybody knew they were saints, or Name
naofa.
Frank Allen, the head of the RPA is a committed Irish speaker - and committed to "Plain English" and "Plain Irish" in the signage.
http://www.rpa.ie/ga/rpa Maidir le naomhóg, ní heol dom. Cuir ceist ar TP nó Domhnall Mac an tSithigh nó saoi éigin sa Chaife Liteartha! Agus cuir an freagra ar fáil anseo, le'd thoil!