Electronic signatures are frequently used in security-critical fields of application such as e-government or e-banking. During the past years, especially server-based signature solutions have gained popularity, as they solve usability problems of traditional client-based approaches. Unfortunately, server-based signature solutions and their underlying security concepts are usually tailored to classical end-user devices such as desktop PCs or laptops. Therefore, these solutions cannot be used on mobile end-user devices such as smartphones. This excludes an increasing number of potential users, who prefer mobile end-user devices to access egovernment and e-banking applications. To solve this problem, we propose a new server-based signature solution that is tailored to the special characteristics of mobile devices. The proposed solution is evaluated by means of a concrete prototype implementation. This prototype proves the feasibility of the proposed solution and demonstrates its capability to leverage the use of electronic signature based applications on mobile end-user devices.