code: function (showSignal) {
          return function (msg) {
              var b = new Buffer(1);
              b.writeUInt8(showSignal ? 1 : 0, 0);
  
              msg.addOption(new Option(Message.Option.URI_PATH, new Buffer("s")));
              msg.addOption(new Option(Message.Option.URI_QUERY, b));
              return msg;
          };
      }
docs: does the special URL writing needed directly to the COAP message object,
  since the URI requires non-text values
  
  @param showSignal
  @returns {Function}