The IETF's Next Steps in Signaling (NSIS) framework provides an up-to-date signaling protocol suite that can be used to dynamically install, maintain, and manipulate state in network nodes. In its two-layered architecture, the General Internet Signaling Transport (GIST) protocol is responsible for the transport and routing of signaling messages. The strong presence of Network Address Translation (NAT) gateways in today's Internet infrastructure causes some major challenges to network signaling protocols like NSIS. The address translation mechanisms performed by common NAT gateways are primarily concerned with address information contained in the IP and transport layer headers. Signaling sessions between two signaling peers do, however, rely on address information contained in GIST data units. If a non GIST-aware NAT gateway merely adapts addresses in the IP and transport headers only, inconsistent state will finally be installed at the signaling nodes. In this paper we present the design, implementation, and evaluation of an application level gateway for the GIST protocol, that translates GIST messages in a way that allows to establish signaling sessions between any two GIST nodes across a NAT gateway.