Sorry but no. If you need signed assemblies you can make your own build from source code and sign it with your own key.
Signed assemblies make upgrade problems and make problems where add on features have to be compiled against specific versions. It also requires that every dependent assembly must also be signed. If I were to suddenly release a new version of mojoPortal with signed assemblies it would break every existing 3rd party feature that is not compiled against the signed assemblies. It would be an upgrade nightmare for anyone with custom features of their own.