Let $Γ=(G, σ)$ be a signed graph of order $n$ with eigenvalues $μ_1,μ_2,\ldots,μ_n.$ We define the Estrada index of a signed graph $Γ$ as $EE(Γ)=\sum_{i=1}^ne^{μ_i}$. We characterize the signed unicyclic graphs with the maximum Estrada index. The signed graph $Γ$ is said to have the pairing property if $μ$ is an eigenvalue whenever $-μ$ is an eigenvalue of $Γ$ and both $μ$ and $-μ$ have the same multiplicities. If $Γ_{p}^-(n, m)$ denotes the set of all unbalanced graphs on $n$ vertices and $m$ edges with the pairing property, we determine the signed graphs having the maximum Estrada index in $Γ_{p}^-(n, m)$, when $m=n$ and $m=n+1$. Finally, we find the signed graphs among all unbalanced complete bipartite signed graphs having the maximum Estrada index.