The full text of this quotation is Certe, Toto, sentio nos in Kansate non iam adesse and it is the Latin translation of You know, Toto, I have a feeling we're not in Kansas anymore, a line from the 1939 classic The Wizard of Oz. On channel, it is used either when Latin is being discussed or to indicate a sudden bewilderment.
It is one of the more oft-quoted examples from satirist Henry Beard's Latin For All Occasions; however I first encountered it in the .sig file of a soc.motss person circa 1992, almost ten years ago, where it was rendered as Certe, Toto, credo nos in Kansate non iam adesse. My knowledge of Latin is virtually nonexistent, but I am guessing that the difference is "...we're not in Kansas..." (credo) as opposed to "...I have a feeling we're not in Kansas..." (sentio). Thanks to sneeper for tipping me off about the Beard book.