Zeta functions of signed graphs

We introduce the zeta function of a signed graph and give a determinant expression for it in terms of the signed oriented line graph, and moreover, we obtain some properties of the zeta function of a signed graph. As applications we affirm the conjecture proposed by Sato [Weighted zeta functions of graph coverings, Electronic J. Combin. 13 (2006), #91] and give a method to construct a family of cospectral signed digraphs. Additionally, we show that two connected regular signed graphs have the same zeta function if and only if they are cospectral.