framework/i18n/Locale.php
public function getCurrencySymbol($currencyCode = null)
    {
        $locale = $this->locale;

        if ($currencyCode !== null) {
            $locale .= '@currency=' . $currencyCode;
        }

        $formatter = new \NumberFormatter($locale, \NumberFormatter::CURRENCY);
        return $formatter->getSymbol(\NumberFormatter::CURRENCY_SYMBOL);
    }
public function getCurrencySymbol($currencyCode = null)
    {
        $locale = $this->locale;

        if ($currencyCode !== null) {
            $locale .= '@currency=' . $currencyCode;
        }

        $formatter = new \NumberFormatter($locale, \NumberFormatter::CURRENCY);
        return $formatter->getSymbol(\NumberFormatter::CURRENCY_SYMBOL);
    }
Returns a currency symbol

@param string $currencyCode the 3-letter ISO 4217 currency code to get symbol for. If null,
method will attempt using currency code from [[locale]].
@return string