code: public MonetaryFormat positiveSign(char positiveSign) {
          checkArgument(!Character.isDigit(positiveSign));
          if (positiveSign == this.positiveSign)
              return this;
          else
              return new MonetaryFormat(negativeSign, positiveSign, zeroDigit, decimalMark, minDecimals, decimalGroups,
                      shift, roundingMode, codes, codeSeparator, codePrefixed);
      }
docs: Set character to prefix positive values. A zero value means no sign is used in this case. For parsing, a missing
  sign will always be interpreted as if the positive sign was used.