The only thing I have ever seen in writing is a letter from the CAA requesting that crews NOT use the term U/S as it is too vague. It went on to say that a concise description of the defect be written so as to aid trouble-shooting.
E.g.
ADF U/S. - Not good!
ADF poor DF, but ident ok. - better.
As far as I know the use of the word 'satis' is 'cause we engineers are all lazy ba**ards and can't be bothered to write the complete word! Plus, when you look at the tiny space in the log book where we are supposed to condense perhaps 10 hrs work into a sensible report it is best to use all the abreviations that one can!
Finally it's 'cause we like to keep the pilots on their toes. Many's the time I have left the cockpit to hear the words 'what the hell does 'XYZ' mean'
