سبحانه و تعالى
Subhanahu wa ta'ala is an Arabic phrase meaning 'glorified and exalted be He'; it is sometimes also translated as 'may He be glorified and exalted'. It refers to Allah, and is generally said (or written) after Allah's name.
In Islamic/Arabic texts it is often abbreviated as SWT, and may be placed in parenthesis after every use of Allah's name. In the Quran and other formal texts, the phrase will probably be written out in full. Whether abbreviated or written in full, using this phrase shows appropriate reverence for Allah.
There are a number of other related expressions and associated abbreviations to show your devotion to Allah and his prophets: 'Azza Wa Jal' (AWJ) 'He is the Mighty and the Majestic'; and 'Jalla Jalaluh' (JJ) 'He is the exalted Majestic'. The common phrase 'Sal Allahu Allahi Wa Salam' (SAW) means 'May the Peace and Blessings of Allah be upon him', and should not be used to refer to Allah (for obvious reasons), and is traditionally used after the the name of the prophet Muhammad.