Electronic signatures play an important role in e-Business and e-Government applications. In particular, electronic signatures fulfilling certain security requirements are legally equivalent to handwritten signatures. Nevertheless, existing signature-creation tools have crucial drawbacks with regard to usability and applicability. To solve these problems, we define appropriate requirements for signature-creation tools to be used in e-Government processes. Taking care of these requirements we propose a modular architecture for adaptable signature-creation tools. Following a user-centered design process we present a concrete implementation of the architecture based upon the Austrian Citizen Card. This implementation has been used to prove the applicability of the architecture in real life. Our tool has been successfully tested and has been assessed as usable and intuitive. It has already been officially released and is widely used in productive environments.