code: function makeCallSignal (signals, opts) {
    return (address, signalName, arg) => {
      if (opts.verbose) {
        console.log('Called signal ' + signalName + ' at [' + address.join(', ') +
                    '].')
      }
      signals.get(address).data.signals[signalName].call(arg)
    }
  }
docs: Return a callSignal function.