public static function get_currency_symbol($currency)
 {
     if (empty($currency)) {
         return false;
     }
     if (!self::$_currency_symbols) {
         self::$_currency_symbols = apply_filters('app-template-currency_symbols', array('AUD' => __('AUD', 'appointments'), 'BRL' => __('BRL', 'appointments'), 'CAD' => __('CAD', 'appointments'), 'CHF' => __('CHF', 'appointments'), 'CZK' => __('CZK', 'appointments'), 'DKK' => __('DKK', 'appointments'), 'EUR' => __('EUR', 'appointments'), 'GBP' => __('GBP', 'appointments'), 'ILS' => __('ILS', 'appointments'), 'HKD' => __('HKD', 'appointments'), 'HUF' => __('HUF', 'appointments'), 'JPY' => __('JPY', 'appointments'), 'MYR' => __('MYR', 'appointments'), 'MXN' => __('MXN', 'appointments'), 'NOK' => __('NOK', 'appointments'), 'NZD' => __('NZD', 'appointments'), 'PHP' => __('PHP', 'appointments'), 'PLN' => __('PLN', 'appointments'), 'SEK' => __('SEK', 'appointments'), 'SGD' => __('SGD', 'appointments'), 'TWD' => __('TWD', 'appointments'), 'THB' => __('THB', 'appointments'), 'TRY' => __('TRY', 'appointments'), 'USD' => __('USD', 'appointments')));
     }
     return !empty(self::$_currency_symbols[$currency]) ? self::$_currency_symbols[$currency] : false;
 }