Expects everything that signature does and also a client type string.
        client can either be master or minion.

def _signature(self, cmd):
        '''
        Expects everything that signature does and also a client type string.
        client can either be master or minion.
        '''
        result = {}

        client = cmd.get('client', 'minion')
        if client == 'minion':
            cmd['fun'] = 'sys.argspec'
            cmd['kwarg'] = dict(module=cmd['module'])
            result = self.run(cmd)
        elif client == 'master':
            parts = cmd['module'].split('.')
            client = parts[0]
            module = '.'.join(parts[1:])  # strip prefix
            if client == 'wheel':
                functions = self.wheelClient.functions
            elif client == 'runner':
                functions = self.runnerClient.functions
            result = {'master': salt.utils.args.argspec_report(functions, module)}
        return result