I wonder whether we read the messages properly before responding. For example the question posed is can we abbreviate "God"? The synonyms of the word "Abbreviate" , according the Thesaurus in Microsoft Word, are "Abridge, condense, curtail cut, , cut short, reduce, shorten, and truncate".
All the above responses do not address the question posed. And I am surprised that CShiva who posed the question has not commented so far. Jagadishprasad has , in fact, given an expansion of the word "God". I would suggest the the abbreviationf "GOD" is "H", which stands for humanity, which is another word for what is repsresented by GOD!!!
Have a nice day.
Narasimhan