What is the bass clef key signature?

Well, if you are asking about key signature, it depends on the key. As in the treble clef, the key of G, for instance, would have one sharp; however the sharp would be on the fourth line because that is where the F is.

If you are asking about the clef, the bass clef (also called the F clef) is essentially a blob of ink on the F line surrounded by a spiral, with two dots (:) to the right, and on either side of the F line. You can see it by going to wikipedia.org and typing "clef" in the search box.