Esalaamu Aleikum wa Rahmat Allah wa Baraketu
These salutations are called
salawat and saying this phrase is seen as an act of devotion towards Allah and sending blessings towards Islamic prophets mentioned in the Qur'an. Saying Allah, subhana wa Ta'al helps us avoid from becoming too casual with His name in conversation, while Muslims are required to say (send blessings) after mentioning the name of the Islamic prophets.
Allah (swt = Subhanahu wa Ta`ala / Praised and exalted is He) The phrase appears after the name of Allah in Islamic texts such as the Qur'an and the Hadith.That is we get it from.
Prophet Muhammad (Saw = Salla Allahu aleihi wa Esalaam/ May Allah bless him and grant him peace) It is also used by Shia Muslims after mentioning Ali ibn Abi Talib or one of the imams that followed Ali.The evidence for sending Salaah on the Prophet Mohammad is not limited to the Qur'an. It is also found in the hadith of the Prophet Muhammad.
"The miser is the one in whose presence I am mentioned, then he does not send the Salah upon me"
This was recorded by Ahmad ibn Hanbal in his Musnad.(=Musnad Ahmad ibn Hanbal is the collection of Hadith collected by the famous Sunni scholar Ibn Hanbal to whom the Hanbali madhab of Sunnis is attributed.)
At-Tirmidhi reported that Abu Hurayrah said:
"The Messenger of Allah said, May he be humiliated, the man in whose presence I am mentioned and he does not send Salaah upon me; may he be humiliated, the man who sees the month of Ramadan come and go, and he is not forgiven; may he be humiliated, the man whose parents live to old age and they do not cause him to be granted admittance to Paradse."
Many of the Islamic Scholars have instructed Muslims not to abbreviate sending the Salah on the Prophet Mohammad (Salla Allahu aleihi wa esalaam), and writing it in abbreviated form does not serve that purpose and is devoid of the virtue of writing 'salla Allaahu aleihi wa esalaam in full. They say the reader may not take notice of it and may not understand what is meant by it. It should also be noted that the symbol used for it is regarded as disapproved by the scholars, who warned against it. I myself have not the Islamic knowledge to know for sure if this is correct or not...Allahu Allem (Allah knows best)...but better safe then sorry I think.
It is advised to also send the Salaah (blessings) on the prophets other than Mohammad (salla Allahu aleihi wa esalaam. Al-Bayhaqi reports that Abu Hurayrah said that the Prophet Muhammad said:
"Send the Salaat on Allah's messengers and prophets for Allah sent them as He sent me."
Finally when mentioning sahaba (the companions of Mohammad), say
radhi Allahu anhu (for males) and
radhi Allahu anha (for females) is used.

I hope that cleared up your question. Ashadu anna la ilaaha antasghfirula ilaik. Please forgive me any mistakes I have. Anything I have or sent to you that is good, is from Allah (subhana wa Ta' la), the mistakes are mine.Jazak Allahu kheiran waleikum esalaam wrt.
[/color] [color="#ff80bf"]Henia