The signature of a knot, σ(K), is equal to σ(V + V^{t}),
the signature of V + V^{t} where V is a Seifert
Matrix for the knot. The signature also equals the signature of the
intersection form on H_{2}(W), where W is the two-fold branched cover of
D^{4} over a pushed-in Seifert surface.

The signature provides bounds for the smooth 4-genus of a knot, for instance, slice knots have signature zero.

**References**

L. Kauffman, and L. Taylor, *Signature of Links,* Trans. Amer. Math.
Soc. **216** (1976), 351-365.

D. Rolfsen, *Knots and Links,* AMS Chelsea Publishing, Providence
(2003)