These are salutations of Salaam and Blessings of God. SAW - Blessings of Allah and His Salaam upon him and his progeny. This is applied to Abraham (SAW) and Muhammad (SAW). All believers are progeny of Abraham. All Believers who have 'Surrendered' (i.e. "Muslim") are progeny of Mohammad. So this is a extended family blessing, directed at the head of the family. SA - Blessings of Allah and His Salaam upon him. This is applied to the Brotherhood of the Messengers and Prophets of God. All of them, as in Isaac (SA). It is also applied to the Ali (SA) and his sons (SA). "The Seers of my community are like the prophets of Israel" (Hadith). RA - God be Pleased/find-Acceptable with him/her. This is for Disciples of Messengers, and Saints of God e.g. Saint Francis (RA), Peter (RA), Joshua (RA), Salaam is ever upon him/her: "Salaam is upon me on the day of my birth, the day that I die, and the day I shall be Raised to Life again" - Jesus speaking in crib Q Sura 19 "Mary" - The word of God testifying to the Purity of the womb that bore It when she was questioned by her family. That last is only for Mary and her son. According to the Prophet, only 2 human beings have ever been (and ever will) come to being in this world untouched by Satan. And they are Mary and her Son. Everyone else -- including the Prophet who was cleansed by Angels and a 'spot' removed from his heart -- needs to go through a cleaning regiment. Hope that answers your questions, and God Knows Best.
SAW = Sala Allah Alihi Wa salam ( Same meaning in Arabic) We are commanded by the Prophet and God to say this after mentioning his name I think that makes sense in context now... apologies again for my ignorance.PBUH = Peace be upon him