Its what you say if you do not know anything about the topic being queried. Its a stronger statement than, "I don't know", don know, or Golly I have no idea about that which you speak. It is a condensed version of the vulgarity, "shit if I know".
Whereas with "Shifino" If said quickly and flatly you may be able to sneak it by even the most erudite snobs. Also good for texting.
" Say Jimmy wherever is your Mother?"
"Gosh Pop, Shifino."
"Well heck Jimmy shifino either, that F***ing b*tch